IEC 60335-2-21:2022

Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters

IEC 60335-2-21:2022 deals with the safety of electric storage water heaters for household and similar purposes and intended for heating water below boiling temperature, their rated voltage being not more than 250 V for single-phase appliances and 480 V for other appliances including direct current (DC) supplied appliances and battery-operated appliances.
This standard also deals with:
– appliances not intended for normal household use, but which nevertheless possibly pose a source of danger to the public, such as appliances intended to be used by laymen in shops and on farms;
– immersion heater units intended to be retrofitted in a heat exchange closed water heater having provision for retrofitting. Additional requirements are given in Annex AA.
As far as is practicable, this standard deals with the common hazards presented by appliances that are encountered by all persons in and around the home. However, in general, it does not take into account
– persons (including children) whose physical, sensory or mental capabilities, or lack of experience and knowledge prevents them from using the appliance safely without supervision or instruction;
– children playing with the appliance.
Attention is drawn to the fact that
– for appliances intended to be used in vehicles or on board ships or aircraft, additional requirements can be necessary;
– in many countries, additional requirements are specified by the national health authorities, the national authorities responsible for the protection of labour and similar authorities;
– in many countries regulations exist for the installation of equipment connected to the water mains.
This standard does not apply to
– appliances for boiling water (IEC 60335-2-15);
– instantaneous water heaters (IEC 60335-2-35);
– commercial dispensing appliances and vending machines (IEC 60335-2-75);
– appliances intended exclusively for industrial purposes;
– appliances intended to be used in locations where special conditions prevail, such as the presence of a corrosive or explosive atmosphere (dust, vapour or gas).
This seventh edition cancels and replaces the sixth edition published in 2012 and Amendment 1:2018. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) the text has been aligned with IEC 60335-1:2020;
b) some notes have been converted to normative text (Clause 1, 5.2, 15.3, 19.1, 19.2, 19.3, 19.4, 22.47, 22.104, 22.110, Annex AA introduction);
c) updated requirement restricting use of appliance inlets (25.1).
This part 2 is to be used in conjunction with the latest edition of IEC 60335-1 and its amendments unless that edition precludes it; in that case, the latest edition that does not preclude it is used. It was established on the basis of the sixth edition (2020) of that standard.

Appareils électrodomestiques et analogues - Sécurité - Partie 2-21: Exigences particulières pour les chauffe-eau à accumulation

L'IEC 60335-2-21:2022 traite de la sécurité des chauffe-eau à accumulation électriques à usage domestique et analogue, destinés au chauffage de l'eau à une température inférieure à la température d'ébullition, dont la tension assignée est inférieure ou égale à 250 V pour les appareils monophasés et à 480 V pour les autres appareils, y compris les appareils alimentés en courant continu et les appareils alimentés par batteries.
La présente norme traite également des:
– appareils non destinés à un usage domestique normal, mais qui peuvent néanmoins constituer une source de danger pour le public, tels que les appareils destinés à être utilisés par des usagers non avertis dans des magasins et des fermes;
– éléments thermoplongeurs destinés à être mis à niveau dans un chauffe-eau fermé à échange thermique prévu pour la mise à niveau. Des exigences supplémentaires sont données à l'Annexe AA.
Dans la mesure du possible, la présente norme traite des dangers courants que présentent les appareils et auxquels sont exposés tous les individus situés à l'intérieur et autour de l'habitation. Cependant, elle ne tient en général pas compte
– des personnes (y compris des enfants) dont les capacités physiques, sensorielles ou mentales; ou le manque d'expérience et de connaissance les empêchent d'utiliser l'appareil en toute sécurité sans surveillance ou instruction;
– des enfants qui jouent avec l'appareil.
L'attention est attirée sur le fait que
– pour les appareils destinés à être utilisés dans des véhicules ou à bord de navires ou d'avions, des exigences supplémentaires peuvent être nécessaires;
– dans de nombreux pays, des exigences supplémentaires sont spécifiées par les organismes nationaux de la santé, par les organismes nationaux responsables de la protection des travailleurs et par des organismes similaires;
– dans de nombreux pays, des réglementations existent pour l'installation des équipements raccordés au réseau d'alimentation en eau.
La présente norme ne s'applique pas
– aux appareils destinés à faire bouillir l'eau (IEC 60335-2-15);
– aux chauffe-eau instantanés (IEC 60335-2-35);
– aux distributeurs commerciaux avec ou sans moyen de paiement (IEC 60335-2-75);
– aux appareils prévus exclusivement pour des usages industriels;
– aux appareils destinés à être utilisés dans des locaux qui présentent des conditions particulières, telles que la présence d'une atmosphère corrosive ou explosive (poussière, vapeur ou gaz).
Cette septième édition annule et remplace la sixième édition parue en 2012 et l'Amendement 1:2018. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) le texte a été aligné sur l'IEC 60335-1:2020;
b) certaines notes ont été converties en texte normatif (Article 1, 5.2, 15.3, 19.1, 19.2, 19.3, 19.4, 22.47, 22.104, 22.110, introduction de l'Annexe AA);
c) l'exigence qui limite l'emploi de socles de connecteurs a été mise à jour (25.1).
La présente partie 2 doit être utilisée conjointement avec la dernière édition de l'IEC 60335-1 et ses amendements sauf si cette édition l'exclut. Dans ce cas, la dernière édition qui n'exclut pas la présente partie 2 est utilisée. Elle a été établie sur la base de la sixième édition (2020) de cette norme.

General Information

• Status: Published
• Publication Date: 17-Oct-2022
• ICS: 13.120 - Domestic safety
• ICS: 91.140.65 - Water heating equipment
• Technical Committee: TC 61 - Safety of household and similar electrical appliances
• Drafting Committee: MT 37 - TC 61/MT 37
• Current Stage: PPUB - Publication issued
• Start Date: 18-Oct-2022
• Completion Date: 18-Nov-2022

Relations

• Revises: IEC 60335-2-21:2012/AMD1:2018 - Amendment 1 - Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters
• Effective Date: 05-Sep-2023
• Revises: IEC 60335-2-21:2012 - Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters
• Effective Date: 05-Sep-2023
• Revises: IEC 60335-2-21:2012/COR1:2013 - Corrigendum 1 - Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters
• Effective Date: 05-Sep-2023

Overview - IEC 60335-2-21:2022 (Storage Water Heaters Safety)

IEC 60335-2-21:2022 is the seventh edition of the IEC safety standard for electric storage water heaters used in households and similar environments. It covers appliances intended to heat water below boiling temperature with rated voltages up to 250 V for single‑phase and 480 V for other appliances (including DC and battery‑operated units). This part 2 document supplements IEC 60335-1 and defines particular safety requirements, test conditions and constructional provisions specific to storage water heaters and certain retrofit immersion heater units (see Annex AA).

Key technical topics and requirements

• Scope and exclusions: Applies to domestic storage water heaters and some non‑household appliances used by laypersons. It excludes boiling/instantaneous water heaters, vending/commercial dispensers, industrial appliances and equipment for special atmospheres.
• Harmonization with IEC 60335-1: Text aligned with IEC 60335-1:2020; Part 2 is intended to be used in conjunction with the latest applicable Part 1 edition.
• Safety and construction: Requirements on construction, insulation, clearances, earthing, internal wiring, and mechanical strength to prevent electric shock, fire and mechanical hazards.
• Thermal protection: Mandatory protections such as thermal cut‑outs and temperature limits; requirements for pressure‑relief devices on closed water heaters (national variations apply).
• Leakage current and dielectric strength: Tests at operating temperature and additional leakage current provisions where applicable.
• Moisture, endurance and abnormal operation tests: Procedures to ensure reliability under expected service conditions.
• Immersion heater retrofit (Annex AA): Normative additional requirements for immersion heater units intended for retrofitting into heat‑exchange closed water heaters.
• Notable changes in 2022 edition:
  • Alignment with IEC 60335-1:2020
  • Several notes converted to normative requirements
  • Updated restriction on appliance inlet use (Clause 25.1)

Practical applications - who uses IEC 60335-2-21

• Manufacturers and OEMs designing and producing electric storage water heaters
• Test laboratories and certification bodies performing type and routine safety tests
• Compliance managers and regulatory authorities ensuring products meet international safety requirements
• Installers and specifiers who need to understand installation and marking requirements
• Product designers and safety engineers addressing thermal, mechanical and electrical hazards

Related standards and considerations

• Must be used together with IEC 60335-1 (general safety requirements for household appliances)
• Excludes appliances covered by IEC 60335-2-15 (boiling water), IEC 60335-2-35 (instantaneous heaters) and IEC 60335-2-75 (vending machines)
• National regulations (installation codes, health and labour authorities) and country‑specific deviations noted in the standard should be considered during design and certification.

Keywords: IEC 60335-2-21, storage water heaters safety, electric storage water heaters, household appliance standard, immersion heater retrofit, IEC 60335-1.

Standards Content (Sample)

IEC 60335-2-21 ®
Edition 7.0 2022-10
COMMENTED VERSION
INTERNATIONAL
STANDARD
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Household and similar electrical appliances – Safety –
Part 2-21: Particular requirements for storage water heaters
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IEC 60335-2-21 ®
Edition 7.0 2022-10
COMMENTED VERSION
INTERNATIONAL
STANDARD
colour
inside
Household and similar electrical appliances – Safety –
Part 2-21: Particular requirements for storage water heaters
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.120; 91.140.65 ISBN 978-2-8322-5897-2

– 2 – IEC 60335-2-21:2022 CMV © IEC 2022
CONTENTS
FOREWORD .4
INTRODUCTION .7
1 Scope .8
2 Normative references .9
3 Terms and definitions .9
4 General requirement . 10
5 General conditions for the tests . 10
6 Classification . 11
7 Marking and instructions . 11
8 Protection against access to live parts . 12
9 Starting of motor-operated appliances . 12
10 Power input and current . 12
11 Heating . 12
12 Void Charging of metal-ion batteries . 13
13 Leakage current and electric strength at operating temperature . 13
14 Transient overvoltages . 13
15 Moisture resistance . 13
16 Leakage current and electric strength . 13
17 Overload protection of transformers and associated circuits . 14
18 Endurance . 14
19 Abnormal operation . 14
20 Stability and mechanical hazards . 15
21 Mechanical strength . 15
22 Construction . 15
23 Internal wiring . 18
24 Components . 18
25 Supply connection and external flexible cords . 19
26 Terminals for external conductors . 19
27 Provision for earthing . 19
28 Screws and connections . 20
29 Clearances, creepage distances and solid insulation . 20
30 Resistance to heat and fire . 20
31 Resistance to rusting. 20
32 Radiation, toxicity and similar hazards . 20

Annexes . 23
Annex A (informative) Routine tests . 23
Annex R (normative) Software evaluation. 24
Annex AA (normative) Additional requirement for immersion heater units intended for
the installation in heat exchange closed water heaters . 25

Bibliography . 28
List of comments . 29

Figure 101 – Examples of types of storage water heaters . 21
Figure 103 102 – Probe for measuring surface temperatures . 22
Figure 102 103 – Example of positions of the thermocouples . 22

Table 101 – Maximum temperature rises of external accessible surfaces under normal
operating conditions . 13

– 4 – IEC 60335-2-21:2022 CMV © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HOUSEHOLD AND SIMILAR ELECTRICAL APPLIANCES –
SAFETY –
Part 2-21: Particular requirements for storage water heaters

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
This commented version (CMV) of the official standard IEC 60335-2-21:2022 edition 7.0
allows the user to identify the changes made to the previous IEC 60335-2-21:2012+
AMD1:2018 CSV edition 6.1. Furthermore, comments from IEC TC 61 experts are provided
to explain the reasons of the most relevant changes, or to clarify any part of the content.
A vertical bar appears in the margin wherever a change has been made. Additions are in
green text, deletions are in strikethrough red text. Experts' comments are identified by a
blue-background number. Mouse over a number to display a pop-up note with the
comment.
This publication contains the CMV and the official standard. The full list of comments is
available at the end of the CMV.

IEC 60335-2-21 has been prepared by IEC technical committee 61: Safety of household and
similar electrical appliances. It is an International Standard.
This seventh edition cancels and replaces the sixth edition published in 2012 and
Amendment 1:2018. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the text has been aligned with IEC 60335-1:2020;
b) some notes have been converted to normative text (Clause 1, 5.2, 15.3, 19.1, 19.2, 19.3,
19.4, 22.47, 22.104, 22.110, Annex AA introduction);
c) updated requirement restricting use of appliance inlets (25.1).
The text of this International Standard is based on the following documents:
Draft Report on voting
61/6675/FDIS 61/6751/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts of the IEC 60335 series, under the general title: Household and similar
electrical appliances – Safety, can be found on the IEC website.
This part 2 is to be used in conjunction with the latest edition of IEC 60335-1 and its
amendments unless that edition precludes it; in that case, the latest edition that does not
preclude it is used. It was established on the basis of the sixth edition (2020) of that standard.
NOTE 1 When "Part 1" is mentioned in this standard, it refers to IEC 60335-1.
This part 2 supplements or modifies the corresponding clauses in IEC 60335-1, so as to convert
that publication into the IEC standard: Particular requirements for storage water heaters.
When a particular subclause of Part 1 is not mentioned in this part 2, that subclause applies as
far as is reasonable. When this standard states "addition", "modification" or "replacement", the
relevant text in Part 1 is to be adapted accordingly.
NOTE 2 The following numbering system is used:
– subclauses, tables and figures that are numbered starting from 101 are additional to those in Part 1;
– unless notes are in a new subclause or involve notes in Part 1, they are numbered starting from 101, including
those in a replaced clause or subclause;
– additional annexes are lettered AA, BB, etc.
NOTE 3 The following print types are used:
– requirements: in roman type;
– test specifications: in italic type;
– notes: in small roman type.
Words in bold in the text are defined in Clause 3. When a definition concerns an adjective, the adjective and the
associated noun are also in bold.

– 6 – IEC 60335-2-21:2022 CMV © IEC 2022
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
NOTE 4 The attention of National Committees is drawn to the fact that equipment manufacturers and testing
organizations may need a transitional period following publication of a new, amended or revised IEC publication in
which to make products in accordance with the new requirements and to equip themselves for conducting new or
revised tests.
It is the recommendation of the committee that the content of this publication be adopted for implementation nationally
not earlier than 12 months or later than 36 months from the date of publication.
The following differences exist in the countries indicated below.
– Clause 1: Immersion heater units intended to be retrofitted in a heat exchange closed water
heater are not allowed unless:
• the immersion heater unit has been tested with the tank models and brands listed in the
instructions of the immersion heater unit;
• the tank models and brands list the models of the immersion heater units that can be
retrofitted (Australia, Netherlands, New Zealand).
– 6.1: Class 0I appliances are allowed (Japan).
– 6.2: IPX0 water heaters are allowed (France).
– 7.1: Additional markings are required (Australia, New Zealand and South Africa).
– 7.12.1: Additional instructions are required (South Africa).
– 13.2: An additional leakage current test is required (China).
– 22.101: Pressure reducing valves have to be designed for an inlet pressure of 2 MPa (South Africa).
– 22.102: The temperature limit is 95 °C (South Africa).
– 22.101: The minimum rated pressure is 1,0 MPa (Denmark, Finland, Norway and Sweden).
– 22.103: Closed water heaters have to incorporate a pressure-relief device sensitive to both
pressure and temperature that operates before the water temperature reaches 99 °C (South
Africa).
– 22.103: Closed water heaters have to incorporate a temperature relief valve or a combined
temperature and pressure-relief valve that operates before the water temperature reaches
100 °C (United Kingdom).
– 22.106: The thermal cut-out of single-phase closed water heaters need only provide single-pole
disconnection (Japan).
– 22.106: For all closed water heaters, the thermal cut-out is to provide all-pole disconnection
(France).
– 22.110: Additional requirements apply to plastic or resin-based containers for open outlet,
cistern type and low pressure type (South Africa).
– 24.1.4 Additional requirements apply to thermal cut-outs (South Africa).
– 24.102: The maximum water temperature is 99 °C (Japan and Norway).
– 24.102: The temperature limit of 130 °C is only allowed for closed water heaters having a rated
pressure of at least 0,4 MPa (South Africa).

IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

INTRODUCTION
It has been assumed in the drafting of this International Standard that the execution of its
provisions is entrusted to appropriately qualified and experienced persons.
Guidance documents concerning the application of the safety requirements for appliances can
be accessed via TC 61 supporting documents on the IEC website
https://www.iec.ch/tc61/supportingdocuments
This information is given for the convenience of users of this International Standard and does
not constitute a replacement for the normative text in this standard.
This standard recognizes the internationally accepted level of protection against hazards such
as electrical, mechanical, thermal, fire and radiation of appliances when operated as in normal
use taking into account the manufacturer's instructions. It also covers abnormal situations that
can be expected in practice and takes into account the way in which electromagnetic
phenomena can affect the safe operation of appliances.
This standard takes into account the requirements of IEC 60364 as far as possible so that there
is compatibility with the wiring rules when the appliance is connected to the supply mains.
However, national wiring rules may can differ.
If an appliance within the scope of this standard also incorporates functions that are covered
by another part 2 of IEC 60335, the relevant part 2 is applied to each function separately, as
far as is reasonable. If applicable, the influence of one function on the other is taken into
account.
When a part 2 standard does not include additional requirements to cover hazards dealt with in
Part 1, Part 1 applies.
NOTE 1 This means that the technical committees responsible for the part 2 standards have determined that it is
not necessary to specify particular requirements for the appliance in question over and above the general
requirements.
This standard is a product family standard dealing with the safety of appliances and takes
precedence over horizontal and generic standards covering the same subject.
NOTE 2 Horizontal and generic standards publications, basic safety publications and group safety publications
covering a hazard are not applicable since they have been taken into consideration when developing the general and
particular requirements for the IEC 60335 series of standards. For example, in the case of temperature requirements
for surfaces on many appliances, generic standards, such as ISO 13732-1 for hot surfaces, are not applicable in
addition to Part 1 or part 2 standards. 1
An appliance that complies with the text of this standard will not necessarily be considered to
comply with the safety principles of the standard if, when examined and tested, it is found to
have other features that impair the level of safety covered by these requirements.
An appliance employing materials or having forms of construction differing from those detailed
in the requirements of this standard may be examined and tested according to the intent of the
requirements and, if found to be substantially equivalent, may be considered to comply with the
standard.
NOTE 3 Standards dealing with non-safety aspects of household appliances are:
– IEC standards published by TC 59 concerning methods of measuring performance;
– CISPR 11, CISPR 14-1 and relevant IEC 61000-3 series standards concerning electromagnetic emissions;
– CISPR 14-2 concerning electromagnetic immunity;
– IEC standards published by TC 111 concerning environmental matters. 2

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HOUSEHOLD AND SIMILAR ELECTRICAL APPLIANCES –
SAFETY –
Part 2-21: Particular requirements for storage water heaters

1 Scope
This clause of Part 1 is replaced by the following.
This part of IEC 60335 deals with the safety of electric storage water heaters for household
and similar purposes and intended for heating water below boiling temperature, their rated
voltage being not more than 250 V for single-phase appliances and 480 V for other appliances
including direct current (DC) supplied appliances and battery-operated appliances. 3
This standard also deals with:
– appliances not intended for normal household use, but which nevertheless may be possibly
pose a source of danger to the public, such as appliances intended to be used by laymen
in shops, in light industry and on farms, are within the scope of this standard;
– This standard is also applicable to immersion heater units intended to be retrofitted in a
heat exchange closed water heater having provision for retrofitting. Such a unit shall
comply with the Additional requirements are given in Annex AA.
NOTE Australia, Netherlands and New Zealand do not allow immersion heater units intended to be retrofitted in
a heat exchange closed water heater unless:
– the immersion heater unit has been tested with the tank models and brands listed in the instructions of the
immersion heater unit;
– the tank models and brands list the models of the immersion heater units that can be retrofitted.
As far as is practicable, this standard deals with the common hazards presented by appliances
that are encountered by all persons in and around the home. However, in general, it does not
take into account
– persons (including children) whose
• physical, sensory or mental capabilities, or
• lack of experience and knowledge
prevents them from using the appliance safely without supervision or instruction;
– children playing with the appliance.
NOTE 101 Attention is drawn to the fact that
– for appliances intended to be used in vehicles or on board ships or aircraft, additional
requirements may can be necessary;
– in many countries, additional requirements are specified by the national health authorities,
the national authorities responsible for the protection of labour and similar authorities;
– in many countries regulations exist for the installation of equipment connected to the water
mains.
NOTE 102 This standard does not apply to
– appliances for boiling water (IEC 60335-2-15);
– instantaneous water heaters (IEC 60335-2-35);
– commercial dispensing appliances and vending machines (IEC 60335-2-75);

– appliances intended exclusively for industrial purposes;
– appliances intended to be used in locations where special conditions prevail, such as the
presence of a corrosive or explosive atmosphere (dust, vapour or gas).
2 Normative references
This clause of Part 1 is applicable except as follows:
Addition:
IEC 60584-1:2013, Thermocouples – Part 1: EMF specifications and tolerances
IEC 60730-1:2013, Automatic electrical controls – Part 1: General requirements
IEC 60730-1:2013/AMD1:2015
IEC 60730-1:2013/AMD2:2020
3 Terms and definitions
This clause of Part 1 is applicable except as follows.
3.1 Definitions relating to physical characteristics
3.1.9 Replacement Addition: 4
normal operation
operation of the appliance after installation in accordance with the instructions and filled with
cold water
3.1071.101
rated pressure
water pressure assigned to the appliance by the manufacturer
3.5 Definitions relating to types of appliances
3.5.101
storage water heater
stationary appliance for heating and storing water in a container and incorporating devices to
control the water temperature
3.5.102
closed water heater
unvented storage water heater intended to operate at the pressure of the water system, the
flow of water being controlled by one or more valves in the outlet system
Note 1 to entry: A closed water heater is shown in Figure 101a).
Note 2 to entry: The operating pressure may be the output pressure of a reducing or boosting device.
3.5.103
cistern-fed water heater
storage water heater that is vented to atmosphere and intended to be supplied by water under
gravity from a separate cistern, the flow of water being controlled by one or more valves in the
outlet system
Note 1 to entry: A cistern-fed water heater is shown in Figure 101d).
Note 2 to entry: The water heater may be installed so that the expanded water returns to the cistern.
n-fed water heater, the pressure in the container results from the column of water in
Note 3 to entry: In a cister
the cistern.
– 10 – IEC 60335-2-21:2022 CMV © IEC 2022
3.5.104
cistern-type water heater
storage water heater having a container supplied by water under gravity from a cistern
incorporated in the appliance
Note 1 to entry: The expanded water can return to the cistern, the flow of water being controlled by one or more
valves in the outlet system.
Note 2 to entry: A cistern-type water heater is shown in Figure 101c).
Note 3 to entry: In a cistern-type water heater, the surface of the water is always at atmospheric pressure.
3.5.105
open-outlet water heater
storage water heater in which the flow of water is only controlled by a valve in the inlet pipe
and in which the expanded or displaced water flows through the outlet
Note 1 to entry: An open-outlet water heater is shown in Figure 101b).
Note 2 to entry: In an open-outlet water heater, the static pressure at the outlet is always at atmospheric pressure.
3.5.106
low-pressure water heater
storage water heater that is vented to atmosphere and intended to be connected to the water
mains through a pressure reducing valve, the flow of water being controlled by one or more
valves in the outlet system
Note 1 to entry: A low-pressure water heater is shown in Figure 101e).
3.1083.5.107
heat exchange water heater
storage water heater in which heated water is fed into a heat exchanger, such as a coiled tube
or similar device, which is itself immersed in a container with the water to be heated
Note 1 to entry: The heated water fed into the heat exchanger is heated from a primary heat source such as a solar
panel or heat pump.
Note 2 to entry: A heat exchange water heater is shown in Figure 101f).
4 General requirement
This clause of Part 1 is applicable.
5 General conditions for the tests
This clause of Part 1 is applicable except as follows.
5.2 Addition:
NOTE 101 Additional appliances can be required if damage occurs during the tests of 19.2 or
19.3.
5.3 Addition:
When the tests are carried out on a single appliance, the tests of 22.47, 22.102, 22.103, and
24.102 are carried out before the tests of Clause 19.

6 Classification
This clause of Part 1 is applicable except as follows.
6.1 Modification:
Water heaters shall be class I, class II or class III.
6.2 Addition:
Water heaters for installation outdoors shall be at least IPX4. Other water heaters shall be at
least IPX1.
7 Marking and instructions
This clause of Part 1 is applicable except as follows.
7.1 Addition:
Appliances, other than cistern-type water heaters, shall be marked with the rated pressure
in pascals.
Appliances shall be marked with the rated capacity in litres.
Closed water heaters shall be marked with a statement that a pressure-relief device is to be
fitted in the installation, unless it is incorporated in the appliance.
Closed water heaters having a rated pressure less than 0,6 MPa and low-pressure water
heaters shall be marked with a statement that a pressure reducing valve is to be fitted in the
installation.
Open-outlet water heaters shall be marked, close to the outlet connection or on a tag attached
to the appliance, with the substance of the following:
WARNING: This outlet acts as a vent and must only be connected to a fitting recommended
by the manufacturer. It must not be connected to a tap.
7.12 Addition:
The instructions for closed water heaters shall state the substance of the following:
from the discharge pipe of the pressure-relief device and that this
– the water may can drip
pipe must be left open to the atmosphere;
– the pressure-relief device is to be operated regularly to remove lime deposits and to verify
that it is not blocked;
– how the water heater can be drained.
7.12.1 Addition:
The installation instructions shall state the substance of the following:
– the type or characteristics of the pressure-relief device and how to connect it, unless it is
incorporated in the appliance;
– a discharge pipe connected to the pressure-relief device is to be installed in a continuously
downward direction and in a frost-free environment;

– 12 – IEC 60335-2-21:2022 CMV © IEC 2022
– the type or characteristics of a pressure reducing valve and the installation details (for
appliances having a rated pressure less than 0,6 MPa).
The instructions for closed water heaters incorporating a heat exchanger shall give details on
the installation of control devices and the temperature settings that are necessary to prevent
operation of the thermal cut-out caused by the heat from the exchanger.
and low-pressure water heaters shall contain
The instructions for cistern-fed water heaters
the substance of the following:
WARNING: Do not connect any pressure-relief device to the vent pipe of this water heater.
7.101 The water inlet and the water outlet shall be identified. This identification shall not be
on detachable parts. If colours are used, blue shall be used for the inlet and red for the outlet.
An alternative means of identification may be by means of arrows showing the direction of the
water flow.
Compliance is checked by inspection.
8 Protection against access to live parts
This clause of Part 1 is applicable.
9 Starting of motor-operated appliances
This clause of Part 1 is not applicable.
10 Power input and current
This clause of Part 1 is applicable.
11 Heating
This clause of Part 1 is applicable except as follows.
11.3 Addition:
Where the external accessible surfaces are suitably flat and access permits, then the test
probe of Figure 102 may be used to measure the temperature rises of external accessible
surfaces specified in Table 101. The probe is applied with a force of 4 N ± 1 N to the surface
in such a way that the best possible contact between the probe and the surface is ensured. The
measurement is performed after a contact period of 30 s.
The probe may be held in place using a laboratory stand clamp or similar device. Any measuring
instrument giving the same results as the probe may be used.
11.7 Replacement Modification: 5
The appliance is operated until steady conditions are established or until the thermostat
interrupts the current for the first time after 16 h, whichever is shorter.
11.8 Modification:
During the test, the temperature rises are monitored continuously and shall not exceed the
values shown in Table 3 and Table 101.
Table 101 – Maximum temperature rises of external accessible surfaces
under normal operating conditions
a
Temperature rise
Surface
K
Bare metal
b
Coated metal
Glass and ceramic
c,d
Plastic and plastic coating > 0,4 mm 62
a
Temperature rises are not measured on:
– tapping connections, pipes, hoses, plumbing fittings, pressure relief valves and sight gauges;
– appliances intended for installation on the roof;
– surfaces not accessible to the 75 mm diameter probe having a hemispherical end.
b
Metal is considered coated when a coating having a minimum thickness of 90 µm made of enamel or non-
substantially plastic coating is used.
c
The temperature rise limit of plastic also applies for plastic material having a metal finish of thickness less
than 0,1 mm.
d
When the thickness of the plastic coating does not exceed 0,4 mm, the temperature rise limits of the coated
metal or of glass and ceramic material apply.

12 Void Charging of metal-ion batteries 6
This clause of Part 1 is applicable.
13 Leakage current and electric strength at operating temperature
This clause of Part 1 is applicable.
14 Transient overvoltages
This clause of Part 1 is applicable.
15 Moisture resistance
This clause of Part 1 is applicable except as follows.
15.2 Addition:
The test is only applicable to cistern-type water heaters.
15.3 Addition:
NOTE 101 If the appliance is too large for the humidity cabinet, the test can be carried out on
those parts that contain electrical components.
16 Leakage current and electric strength
This clause of Part 1 is applicable.

– 14 – IEC 60335-2-21:2022 CMV © IEC 2022
17 Overload protection of transformers and associated circuits
This clause of Part 1 is applicable.
18 Endurance
This clause of Part 1 is not applicable.
19 Abnormal operation
This clause of Part 1 is applicable except as follows.
19.1 Modification:
Instead of the tests specified for appliances incorporating heating elements, the following
applies.
For closed water heaters, low-pressure water heaters and open-outlet water heaters,
compliance is checked by the tests of 19.2, 19.3 and 19.4 if applicable. However, 19.101 applies
instead for appliances not liable to be emptied in normal use and having all four of the following
features:
– an outer enclosure of metal, except for the cover used for the supply terminals and controls
that may be non-metallic, or a water container of metal and an outer enclosure of non-
metallic material;
NOTE 101 Non-metallic covers can be used for the supply terminals and controls.
– non-combustible thermal insulation;
NOTE 102 Insulation withstanding the needle flame test of Annex E is considered to be non-combustible.
– a capacity exceeding 30 l;
– a rated power input not exceeding 6 kW.
NOTE 103 Appliances are not considered liable to be emptied in normal use if emptying through
the inlet is prevented by a check valve, a pipe interrupter or an air gap. These devices can may
be fitted in the inlet pipe in accordance with the instructions. Emptying through openings
provided for servicing purposes only is not considered to be normal use.
Thermal insulation complying with the needle flame test of normative Annex E is considered to
be non-combustible.
NOTE 104 Cistern-fed water heaters and cistern-type water heaters are not subjected to the
tests specified for appliances incorporating heating elements. 7
19.2 Addition:
The appliance is operated empty, any thermal control that operates during the test of Clause 11
being short-circuited.
NOTE 101 If the appliance is provided with more than one thermal control, these are short-
circuited in turn.
19.3 Addition:
NOTE 101 If the water heater has been damaged during the previous test, a new appliance is
used.
19.4 Replacement:
For open-outlet water heaters, the test of 19.2 is repeated but with the container filled with
water to a level at least 10 mm above the highest point of the heating element. The appliance
is operated at 1,15 times rated power input under normal operation.
NOTE 101 If the water heater has been damaged during previous tests, a new appliance is used.
19.13 Addition:
There shall be no leakage from the container during the tests.
19.101 The appliance is tested for 24 h under the conditions specified in Clause 11 but with
the container empty.
20 Stability and mechanical hazards
This clause of Part 1 is applicable.
21 Mechanical strength
This clause of Part 1 is applicable.
22 Construction
This clause of Part 1 is applicable except as follows.
22.6 Addition:
The enclosure shall have a drain hole positioned so that the water can drain without impairing
electrical insulation, unless condensed water cannot accumulate within the enclosure in normal
use. The hole shall be at least 5 mm in diameter or 20 mm in area with a width of at least
3 mm. Holes that do not meet these dimensions are considered to be blocked when determining
compliance. 8
Compliance is checked by inspection and measurement.
22.20 Addition:
Thermal insulation shall not be used for basic insulation of internal wiring.
22.47 Replacement:
Appliances shall withstand the water pressure occurring in normal use.
Compliance is checked by subjecting the appliance to a water pressure of
– twice the rated pressure, for closed water heaters. If the water heater is supplied through
a pressure reducing valve, the container is instead subjected to twice the maximum working
pressure in the container during the test of Clause 11;
NOTE 101 The pressure reducing valve can be incorporated in the water-inlet pipe.
NOTE 2 The working pressure is the maximum pressure in the container measured during the test of Clause 11.

– 16 – IEC 60335-2-21:2022 CMV © IEC 2022
– 1,5 times rated pressure, for cistern-fed water heaters and low-pressure water heaters;
– 0,15 MPa, for open-outlet water heaters;
– 0,03 MPa, for cistern-type water heaters.
Heat exchangers incorporated in an appliance are subjected to a pressure test based on the
maximum working pressure in the heat exchanger during the test of Clause 11.
Pressure-relief devices are rendered inoperative. The pressure is raised at a rate of 0,13 MPa/s
to the specified value and is maintained at that value for 15 min.
Water shall not leak from the appliance and there shall be no permanent deformation to such
an extent that compliance with this standard is impaired.
NOTE 3 Heat exchangers incorporated in an appliance are subjected to a pressure test based on their working
pressure.
NOTE 4 Damage to a protective coating on the inside of containers is not considered to be a
hazard.
22.101 The rated pressure of closed water heaters intended for direct connection to the
water main shall be at least 0,6 MPa.
The rated pressure of closed water heaters and low-pressure water heaters, intended to be
supplied by a pressure reducing valve that is not incorporated in the appliance, shall be at least
0,1 MPa.
The rated pressure of cistern-fed water heaters shall not exceed 0,2 MPa.
NOTE The rated pressure of open-outlet water heaters is 0 Pa.
Compliance is checked by inspection.
22.102 Closed water heaters shall be constructed so that repeated drawing off does not
cause the water to boil.
Compliance is checked by the following test.
The appliance is operated as specified in Clause 11.
When the thermostat has operated for the first time, water is drawn off at a rate of
approximately 2 l/min or 10 % of the capacity of the appliance per minute, whichever is less,
until the thermostat switches on again.
When the thermostat next operates, water is drawn off again at the same rate until the
thermostat switches on, this sequence being repeated until steady conditions are established.
The temperature of the water, measured by means of a thermocouple at the outlet, shall not
exceed 98 °C.
22.103 Pressure-relief devices of closed water heaters shall prevent the pressure in the
container from exceeding the rated pressure by more than 0,1 MPa.
Compliance is checked by subjecting the container to a slowly increasing water pressure.
NOTE The pressure-relief device can be fitted during installation.

22.104 The outlet of open-outlet water heaters shall be constructed so that the water flow is
not limited to such an extent that the container is subjected to a significant pressure.
NOTE This requirement is considered to be met if the cross-sectional area of the water outlet
is not less than that of the inlet.
The vent pipe of low pressure water heaters shall have an internal diameter of at least 20 mm.
Compliance is checked by inspection and measurement.
22.105 Cistern-type water heaters shall be constructed so that the container is always at
atmospheric pressure by means of a vent having an area of at least 30 mm and a minimum
dimension of at least 3 mm.
Compliance is checked by inspection and by measurement.
22.106 Closed water heaters shall incorporate a thermal cut-out providing all-pole
disconnection and which operates independently from the thermostat. However, for
appliances intended to be connected to fixed wiring, the neutral conductor need not be
disconnected.
Compliance is checked by inspection.
22.107 Heating elements and thermal control sensors in contact with the outer surface of the
container shall be held in position securely.
Compliance is checked by inspection.
22.108 Appliances for wall mounting shall have reliable provision for fixing to a wall,
independent of the connection to the water mains.
Compliance is checked by inspection.
22.109 Appliances having a capacity of more than 15 l that cannot be emptied through a drain
fitted in the water pipes shall incorporate means for drainin
...

IEC 60335-2-21 ®
Edition 7.0 2022-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Household and similar electrical appliances – Safety –
Part 2-21: Particular requirements for storage water heaters

Appareils électrodomestiques et analogues – Sécurité –
Partie 2-21: Exigences particulières pour les chauffe-eau à accumulation

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IEC 60335-2-21 ®
Edition 7.0 2022-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Household and similar electrical appliances – Safety –

Part 2-21: Particular requirements for storage water heaters

Appareils électrodomestiques et analogues – Sécurité –

Partie 2-21: Exigences particulières pour les chauffe-eau à accumulation

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 13.120; 91.140.65 ISBN 978-2-8322-5858-3

– 2 – IEC 60335-2-21:2022 © IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 9
3 Terms and definitions . 9
4 General requirement . 10
5 General conditions for the tests . 10
6 Classification . 10
7 Marking and instructions . 11
8 Protection against access to live parts . 12
9 Starting of motor-operated appliances . 12
10 Power input and current . 12
11 Heating . 12
12 Charging of metal-ion batteries . 13
13 Leakage current and electric strength at operating temperature . 13
14 Transient overvoltages . 13
15 Moisture resistance . 13
16 Leakage current and electric strength . 13
17 Overload protection of transformers and associated circuits . 14
18 Endurance . 14
19 Abnormal operation . 14
20 Stability and mechanical hazards . 15
21 Mechanical strength . 15
22 Construction . 15
23 Internal wiring . 17
24 Components . 18
25 Supply connection and external flexible cords . 19
26 Terminals for external conductors . 19
27 Provision for earthing . 19
28 Screws and connections . 19
29 Clearances, creepage distances and solid insulation . 20
30 Resistance to heat and fire . 20
31 Resistance to rusting . 20
32 Radiation, toxicity and similar hazards . 20
Annexes . 23
Annex A (informative) Routine tests . 23
Annex R (normative) Software evaluation . 24
Annex AA (normative) Additional requirement for immersion heater units intended for
the installation in heat exchange closed water heaters . 25
Bibliography . 28

Figure 101 – Examples of types of storage water heaters . 21
Figure 102 – Probe for measuring surface temperatures . 22
Figure 103 – Example of positions of the thermocouples . 22

Table 101 – Maximum temperature rises of external accessible surfaces under normal
operating conditions . 13

– 4 – IEC 60335-2-21:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HOUSEHOLD AND SIMILAR ELECTRICAL APPLIANCES –
SAFETY –
Part 2-21: Particular requirements for storage water heaters

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 60335-2-21 has been prepared by IEC technical committee 61: Safety of household and
similar electrical appliances. It is an International Standard.
This seventh edition cancels and replaces the sixth edition published in 2012 and
Amendment 1:2018. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the text has been aligned with IEC 60335-1:2020;
b) some notes have been converted to normative text (Clause 1, 5.2, 15.3, 19.1, 19.2, 19.3,
19.4, 22.47, 22.104, 22.110, Annex AA introduction);
c) updated requirement restricting use of appliance inlets (25.1).

The text of this International Standard is based on the following documents:
Draft Report on voting
61/6675/FDIS 61/6751/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts of the IEC 60335 series, under the general title: Household and similar
electrical appliances – Safety, can be found on the IEC website.
This part 2 is to be used in conjunction with the latest edition of IEC 60335-1 and its
amendments unless that edition precludes it; in that case, the latest edition that does not
preclude it is used. It was established on the basis of the sixth edition (2020) of that standard.
NOTE 1 When "Part 1" is mentioned in this standard, it refers to IEC 60335-1.
This part 2 supplements or modifies the corresponding clauses in IEC 60335-1, so as to convert
that publication into the IEC standard: Particular requirements for storage water heaters.
When a particular subclause of Part 1 is not mentioned in this part 2, that subclause applies as
far as is reasonable. When this standard states "addition", "modification" or "replacement", the
relevant text in Part 1 is to be adapted accordingly.
NOTE 2 The following numbering system is used:
– subclauses, tables and figures that are numbered starting from 101 are additional to those in Part 1;
– unless notes are in a new subclause or involve notes in Part 1, they are numbered starting from 101, including
those in a replaced clause or subclause;
– additional annexes are lettered AA, BB, etc.
NOTE 3 The following print types are used:
– requirements: in roman type;
– test specifications: in italic type;
– notes: in small roman type.
Words in bold in the text are defined in Clause 3. When a definition concerns an adjective, the adjective and the
associated noun are also in bold.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 60335-2-21:2022 © IEC 2022
NOTE 4 The attention of National Committees is drawn to the fact that equipment manufacturers and testing
organizations may need a transitional period following publication of a new, amended or revised IEC publication in
which to make products in accordance with the new requirements and to equip themselves for conducting new or
revised tests.
It is the recommendation of the committee that the content of this publication be adopted for implementation nationally
not earlier than 12 months or later than 36 months from the date of publication.
The following differences exist in the countries indicated below.
– Clause 1: Immersion heater units intended to be retrofitted in a heat exchange closed water
heater are not allowed unless:
• the immersion heater unit has been tested with the tank models and brands listed in the
instructions of the immersion heater unit;
• the tank models and brands list the models of the immersion heater units that can be
retrofitted (Australia, Netherlands, New Zealand).
– 6.1: Class 0I appliances are allowed (Japan).
– 6.2: IPX0 water heaters are allowed (France).
– 7.1: Additional markings are required (Australia, New Zealand and South Africa).
– 7.12.1: Additional instructions are required (South Africa).
– 13.2: An additional leakage current test is required (China).
– 22.101: Pressure reducing valves have to be designed for an inlet pressure of 2 MPa (South
Africa).
– 22.102: The temperature limit is 95 °C (South Africa).
– 22.101: The minimum rated pressure is 1,0 MPa (Denmark, Finland, Norway and Sweden).
– 22.103: Closed water heaters have to incorporate a pressure-relief device sensitive to both
pressure and temperature that operates before the water temperature reaches 99 °C (South
Africa).
– 22.103: Closed water heaters have to incorporate a temperature relief valve or a combined
temperature and pressure-relief valve that operates before the water temperature reaches
100 °C (United Kingdom).
– 22.106: The thermal cut-out of single-phase closed water heaters need only provide single-
pole disconnection (Japan).
– 22.106: For all closed water heaters, the thermal cut-out is to provide all-pole disconnection
(France).
– 22.110: Additional requirements apply to plastic or resin-based containers for open outlet,
cistern type and low pressure type (South Africa).
– 24.1.4 Additional requirements apply to thermal cut-outs (South Africa).
– 24.102: The maximum water temperature is 99 °C (Japan and Norway).
– 24.102: The temperature limit of 130 °C is only allowed for closed water heaters having a
rated pressure of at least 0,4 MPa (South Africa).

INTRODUCTION
It has been assumed in the drafting of this International Standard that the execution of its
provisions is entrusted to appropriately qualified and experienced persons.
Guidance documents concerning the application of the safety requirements for appliances can
be accessed via TC 61 supporting documents on the IEC website
https://www.iec.ch/tc61/supportingdocuments
This information is given for the convenience of users of this International Standard and does
not constitute a replacement for the normative text in this standard.
This standard recognizes the internationally accepted level of protection against hazards such
as electrical, mechanical, thermal, fire and radiation of appliances when operated as in normal
use taking into account the manufacturer's instructions. It also covers abnormal situations that
can be expected in practice and takes into account the way in which electromagnetic
phenomena can affect the safe operation of appliances.
This standard takes into account the requirements of IEC 60364 as far as possible so that there
is compatibility with the wiring rules when the appliance is connected to the supply mains.
However, national wiring rules can differ.
If an appliance within the scope of this standard also incorporates functions that are covered
by another part 2 of IEC 60335, the relevant part 2 is applied to each function separately, as
far as is reasonable. If applicable, the influence of one function on the other is taken into
account.
When a part 2 standard does not include additional requirements to cover hazards dealt with in
Part 1, Part 1 applies.
NOTE 1 This means that the technical committees responsible for the part 2 standards have determined that it is
not necessary to specify particular requirements for the appliance in question over and above the general
requirements.
This standard is a product family standard dealing with the safety of appliances and takes
precedence over horizontal and generic standards covering the same subject.
NOTE 2 Horizontal publications, basic safety publications and group safety publications covering a hazard are not
applicable since they have been taken into consideration when developing the general and particular requirements
for the IEC 60335 series of standards.
An appliance that complies with the text of this standard will not necessarily be considered to
comply with the safety principles of the standard if, when examined and tested, it is found to
have other features that impair the level of safety covered by these requirements.
An appliance employing materials or having forms of construction differing from those detailed
in the requirements of this standard may be examined and tested according to the intent of the
requirements and, if found to be substantially equivalent, may be considered to comply with the
standard.
NOTE 3 Standards dealing with non-safety aspects of household appliances are:
– IEC standards published by TC 59 concerning methods of measuring performance;
– CISPR 11, CISPR 14-1 and relevant IEC 61000-3 series standards concerning electromagnetic emissions;
– CISPR 14-2 concerning electromagnetic immunity;
– IEC standards published by TC 111 concerning environmental matters.

– 8 – IEC 60335-2-21:2022 © IEC 2022
HOUSEHOLD AND SIMILAR ELECTRICAL APPLIANCES –
SAFETY –
Part 2-21: Particular requirements for storage water heaters

1 Scope
This clause of Part 1 is replaced by the following.
This part of IEC 60335 deals with the safety of electric storage water heaters for household
and similar purposes and intended for heating water below boiling temperature, their rated
voltage being not more than 250 V for single-phase appliances and 480 V for other appliances
including direct current (DC) supplied appliances and battery-operated appliances.
This standard also deals with:
– appliances not intended for normal household use, but which nevertheless possibly pose a
source of danger to the public, such as appliances intended to be used by laymen in shops
and on farms;
– immersion heater units intended to be retrofitted in a heat exchange closed water heater
having provision for retrofitting. Additional requirements are given in Annex AA.
As far as is practicable, this standard deals with the common hazards presented by appliances
that are encountered by all persons in and around the home. However, in general, it does not
take into account
– persons (including children) whose
• physical, sensory or mental capabilities, or
• lack of experience and knowledge
prevents them from using the appliance safely without supervision or instruction;
– children playing with the appliance.
Attention is drawn to the fact that
– for appliances intended to be used in vehicles or on board ships or aircraft, additional
requirements can be necessary;
– in many countries, additional requirements are specified by the national health authorities,
the national authorities responsible for the protection of labour and similar authorities;
– in many countries regulations exist for the installation of equipment connected to the water
mains.
This standard does not apply to
– appliances for boiling water (IEC 60335-2-15);
– instantaneous water heaters (IEC 60335-2-35);
– commercial dispensing appliances and vending machines (IEC 60335-2-75);
– appliances intended exclusively for industrial purposes;
– appliances intended to be used in locations where special conditions prevail, such as the
presence of a corrosive or explosive atmosphere (dust, vapour or gas).

2 Normative references
This clause of Part 1 is applicable except as follows:
Addition:
IEC 60584-1, Thermocouples – Part 1: EMF specifications and tolerances
IEC 60730-1:2013, Automatic electrical controls – Part 1: General requirements
IEC 60730-1:2013/AMD1:2015
IEC 60730-1:2013/AMD2:2020
3 Terms and definitions
This clause of Part 1 is applicable except as follows.
3.1 Definitions relating to physical characteristics
3.1.9 Addition:
operation of the appliance after installation in accordance with the instructions and filled with
cold water
3.1.101
rated pressure
water pressure assigned to the appliance by the manufacturer
3.5 Definitions relating to types of appliances
3.5.101
storage water heater
stationary appliance for heating and storing water in a container and incorporating devices to
control the water temperature
3.5.102
closed water heater
unvented storage water heater intended to operate at the pressure of the water system, the
flow of water being controlled by one or more valves in the outlet system
Note 1 to entry: A closed water heater is shown in Figure 101a).
Note 2 to entry: The operating pressure may be the output pressure of a reducing or boosting device.
3.5.103
cistern-fed water heater
storage water heater that is vented to atmosphere and intended to be supplied by water under
gravity from a separate cistern, the flow of water being controlled by one or more valves in the
outlet system
Note 1 to entry: A cistern-fed water heater is shown in Figure 101d).
Note 2 to entry: The water heater may be installed so that the expanded water returns to the cistern.
Note 3 to entry: In a cistern-fed water heater, the pressure in the container results from the column of water in
the cistern.
– 10 – IEC 60335-2-21:2022 © IEC 2022
3.5.104
cistern-type water heater
storage water heater having a container supplied by water under gravity from a cistern
incorporated in the appliance
Note 1 to entry: The expanded water can return to the cistern, the flow of water being controlled by one or more
valves in the outlet system.
Note 2 to entry: A cistern-type water heater is shown in Figure 101c).
Note 3 to entry: In a cistern-type water heater, the surface of the water is always at atmospheric pressure.
3.5.105
open-outlet water heater
storage water heater in which the flow of water is only controlled by a valve in the inlet pipe
and in which the expanded or displaced water flows through the outlet
Note 1 to entry: An open-outlet water heater is shown in Figure 101b).
Note 2 to entry: In an open-outlet water heater, the static pressure at the outlet is always at atmospheric pressure.
3.5.106
low-pressure water heater
storage water heater that is vented to atmosphere and intended to be connected to the water
mains through a pressure reducing valve, the flow of water being controlled by one or more
valves in the outlet system
Note 1 to entry: A low-pressure water heater is shown in Figure 101e).
3.5.107
heat exchange water heater
storage water heater in which heated water is fed into a heat exchanger, such as a coiled tube
or similar device, which is itself immersed in a container with the water to be heated
Note 1 to entry: The heated water fed into the heat exchanger is heated from a primary heat source such as a solar
panel or heat pump.
Note 2 to entry: A heat exchange water heater is shown in Figure 101f).
4 General requirement
This clause of Part 1 is applicable.
5 General conditions for the tests
This clause of Part 1 is applicable except as follows.
5.2 Addition:
Additional appliances can be required if damage occurs during the tests of 19.2 or 19.3.
5.3 Addition:
When the tests are carried out on a single appliance, the tests of 22.47, 22.102, 22.103, and
24.102 are carried out before the tests of Clause 19.
6 Classification
This clause of Part 1 is applicable except as follows.

6.1 Modification:
Water heaters shall be class I, class II or class III.
6.2 Addition:
Water heaters for installation outdoors shall be at least IPX4. Other water heaters shall be at
least IPX1.
7 Marking and instructions
This clause of Part 1 is applicable except as follows.
7.1 Addition:
Appliances, other than cistern-type water heaters, shall be marked with the rated pressure
in pascals.
Appliances shall be marked with the rated capacity in litres.
Closed water heaters shall be marked with a statement that a pressure-relief device is to be
fitted in the installation, unless it is incorporated in the appliance.
Closed water heaters having a rated pressure less than 0,6 MPa and low-pressure water
heaters shall be marked with a statement that a pressure reducing valve is to be fitted in the
installation.
Open-outlet water heaters shall be marked, close to the outlet connection or on a tag attached
to the appliance, with the substance of the following:
WARNING: This outlet acts as a vent and must only be connected to a fitting recommended
by the manufacturer. It must not be connected to a tap.
7.12 Addition:
The instructions for closed water heaters shall state the substance of the following:
– the water can drip from the discharge pipe of the pressure-relief device and that this pipe
must be left open to the atmosphere;
– the pressure-relief device is to be operated regularly to remove lime deposits and to verify
that it is not blocked;
– how the water heater can be drained.
7.12.1 Addition:
The installation instructions shall state the substance of the following:
– the type or characteristics of the pressure-relief device and how to connect it, unless it is
incorporated in the appliance;
– a discharge pipe connected to the pressure-relief device is to be installed in a continuously
downward direction and in a frost-free environment;
– the type or characteristics of a pressure reducing valve and the installation details (for
appliances having a rated pressure less than 0,6 MPa).

– 12 – IEC 60335-2-21:2022 © IEC 2022
The instructions for closed water heaters incorporating a heat exchanger shall give details on
the installation of control devices and the temperature settings that are necessary to prevent
operation of the thermal cut-out caused by the heat from the exchanger.
The instructions for cistern-fed water heaters and low-pressure water heaters shall contain
the substance of the following:
WARNING: Do not connect any pressure-relief device to the vent pipe of this water heater.
7.101 The water inlet and the water outlet shall be identified. This identification shall not be
on detachable parts. If colours are used, blue shall be used for the inlet and red for the outlet.
An alternative means of identification may be by means of arrows showing the direction of the
water flow.
Compliance is checked by inspection.
8 Protection against access to live parts
This clause of Part 1 is applicable.
9 Starting of motor-operated appliances
This clause of Part 1 is not applicable.
10 Power input and current
This clause of Part 1 is applicable.
11 Heating
This clause of Part 1 is applicable except as follows.
11.3 Addition:
Where the external accessible surfaces are suitably flat and access permits, then the test
probe of Figure 102 may be used to measure the temperature rises of external accessible
surfaces specified in Table 101. The probe is applied with a force of 4 N ± 1 N to the surface
in such a way that the best possible contact between the probe and the surface is ensured. The
measurement is performed after a contact period of 30 s.
The probe may be held in place using a laboratory stand clamp or similar device. Any measuring
instrument giving the same results as the probe may be used.
11.7 Modification:
The appliance is operated until steady conditions are established or until the thermostat
interrupts the current for the first time after 16 h, whichever is shorter.
11.8 Modification:
During the test, the temperature rises are monitored continuously and shall not exceed the
values shown in Table 3 and Table 101.

Table 101 – Maximum temperature rises of external accessible surfaces
under normal operating conditions
a
Temperature rise
Surface
K
Bare metal
b
Coated metal 49
Glass and ceramic
c,d
Plastic and plastic coating > 0,4 mm 62
a
Temperature rises are not measured on:
– tapping connections, pipes, hoses, plumbing fittings, pressure relief valves and sight gauges;
– appliances intended for installation on the roof;
– surfaces not accessible to the 75 mm diameter probe having a hemispherical end.
b
Metal is considered coated when a coating having a minimum thickness of 90 µm made of enamel or non-
substantially plastic coating is used.
c
The temperature rise limit of plastic also applies for plastic material having a metal finish of thickness less
than 0,1 mm.
d
When the thickness of the plastic coating does not exceed 0,4 mm, the temperature rise limits of the coated
metal or of glass and ceramic material apply.

12 Charging of metal-ion batteries
This clause of Part 1 is applicable.
13 Leakage current and electric strength at operating temperature
This clause of Part 1 is applicable.
14 Transient overvoltages
This clause of Part 1 is applicable.
15 Moisture resistance
This clause of Part 1 is applicable except as follows.
15.2 Addition:
The test is only applicable to cistern-type water heaters.
15.3 Addition:
If the appliance is too large for the humidity cabinet, the test can be carried out on those parts
that contain electrical components.
16 Leakage current and electric strength
This clause of Part 1 is applicable.

– 14 – IEC 60335-2-21:2022 © IEC 2022
17 Overload protection of transformers and associated circuits
This clause of Part 1 is applicable.
18 Endurance
This clause of Part 1 is not applicable.
19 Abnormal operation
This clause of Part 1 is applicable except as follows.
19.1 Modification:
Instead of the tests specified for appliances incorporating heating elements, the following
applies.
For closed water heaters, low-pressure water heaters and open-outlet water heaters,
compliance is checked by the tests of 19.2, 19.3 and 19.4 if applicable. However, 19.101 applies
instead for appliances not liable to be emptied in normal use and having all four of the following
features:
– an outer enclosure of metal, except for the cover used for the supply terminals and controls
that may be non-metallic, or a water container of metal and an outer enclosure of non-
metallic material;
– non-combustible thermal insulation;
– a capacity exceeding 30 l;
– a rated power input not exceeding 6 kW.
Appliances are not considered liable to be emptied in normal use if emptying through the inlet
is prevented by a check valve, a pipe interrupter or an air gap. These devices may be fitted in
the inlet pipe in accordance with the instructions. Emptying through openings provided for
servicing purposes only is not considered to be normal use.
Thermal insulation complying with the needle flame test of normative Annex E is considered to
be non-combustible.
Cistern-fed water heaters and cistern-type water heaters are not subjected to the tests
specified for appliances incorporating heating elements.
19.2 Addition:
The appliance is operated empty, any thermal control that operates during the test of Clause 11
being short-circuited.
If the appliance is provided with more than one thermal control, these are short-circuited in turn.
19.3 Addition:
If the water heater has been damaged during the previous test, a new appliance is used.

19.4 Replacement:
For open-outlet water heaters, the test of 19.2 is repeated but with the container filled with
water to a level at least 10 mm above the highest point of the heating element. The appliance
is operated at 1,15 times rated power input under normal operation.
If the water heater has been damaged during previous tests, a new appliance is used.
19.13 Addition:
There shall be no leakage from the container during the tests.
19.101 The appliance is tested for 24 h under the conditions specified in Clause 11 but with
the container empty.
20 Stability and mechanical hazards
This clause of Part 1 is applicable.
21 Mechanical strength
This clause of Part 1 is applicable.
22 Construction
This clause of Part 1 is applicable except as follows.
22.6 Addition:
The enclosure shall have a drain hole positioned so that the water can drain without impairing
electrical insulation, unless condensed water cannot accumulate within the enclosure in normal
use. The hole shall be at least 5 mm in diameter or 20 mm in area with a width of at least
3 mm. Holes that do not meet these dimensions are considered to be blocked when determining
compliance.
Compliance is checked by inspection and measurement.
22.20 Addition:
Thermal insulation shall not be used for basic insulation of internal wiring.
22.47 Replacement:
Appliances shall withstand the water pressure occurring in normal use.
Compliance is checked by subjecting the appliance to a water pressure of
– twice the rated pressure, for closed water heaters. If the water heater is supplied through
a pressure reducing valve, the container is instead subjected to twice the maximum working
pressure in the container during the test of Clause 11;
NOTE 101 The pressure reducing valve can be incorporated in the water-inlet pipe.
– 1,5 times rated pressure, for cistern-fed water heaters and low-pressure water heaters;
– 0,15 MPa, for open-outlet water heaters;

– 16 – IEC 60335-2-21:2022 © IEC 2022
– 0,03 MPa, for cistern-type water heaters.
Heat exchangers incorporated in an appliance are subjected to a pressure test based on the
maximum working pressure in the heat exchanger during the test of Clause 11.
Pressure-relief devices are rendered inoperative. The pressure is raised at a rate of 0,13 MPa/s
to the specified value and is maintained at that value for 15 min.
Water shall not leak from the appliance and there shall be no permanent deformation to such
an extent that compliance with this standard is impaired.
Damage to a protective coating on the inside of containers is not considered to be a hazard.
22.101 The rated pressure of closed water heaters intended for direct connection to the
water main shall be at least 0,6 MPa.
The rated pressure of closed water heaters and low-pressure water heaters, intended to be
supplied by a pressure reducing valve that is not incorporated in the appliance, shall be at least
0,1 MPa.
The rated pressure of cistern-fed water heaters shall not exceed 0,2 MPa.
NOTE The rated pressure of open-outlet water heaters is 0 Pa.
Compliance is checked by inspection.
22.102 Closed water heaters shall be constructed so that repeated drawing off does not
cause the water to boil.
Compliance is checked by the following test.
The appliance is operated as specified in Clause 11.
When the thermostat has operated for the first time, water is drawn off at a rate of
approximately 2 l/min or 10 % of the capacity of the appliance per minute, whichever is less,
until the thermostat switches on again.
When the thermostat next operates, water is drawn off again at the same rate until the
thermostat switches on, this sequence being repeated until steady conditions are established.
The temperature of the water, measured by means of a thermocouple at the outlet, shall not
exceed 98 °C.
22.103 Pressure-relief devices of closed water heaters shall prevent the pressure in the
container from exceeding the rated pressure by more than 0,1 MPa.
Compliance is checked by subjecting the container to a slowly increasing water pressure.
NOTE The pressure-relief device can be fitted during installation.
22.104 The outlet of open-outlet water heaters shall be constructed so that the water flow is
not limited to such an extent that the container is subjected to a significant pressure. This
requirement is considered to be met if the cross-sectional area of the water outlet is not less
than that of the inlet.
The vent pipe of low pressure water heaters shall have an internal diameter of at least 20 mm.

Compliance is checked by inspection and measurement.
22.105 Cistern-type water heaters shall be constructed so that the container is always at
atmospheric pressure by means of a vent having an area of at least 30 mm and a minimum
dimension of at least 3 mm.
Compliance is checked by inspection and by measurement.
22.106 Closed water heaters shall incorporate a thermal cut-out providing all-pole
disconnection and which operates independently from the thermostat. However, for
appliances intended to be connected to fixed wiring, the neutral conductor need not be
disconnected.
Compliance is checked by inspection.
22.107 Heating elements and thermal control sensors in contact with the
...