ISO 23551-8:2023

Safety and control devices for gas burners and gas-burning appliances — Particular requirements — Part 8: Multifunctional controls

This document specifies safety, construction, performance and testing requirements of multifunctional controls (MFC) intended for use with gas burners, gas appliances and appliances of similar use. This document applies to an MFC with declared maximum inlet pressures up to and including 50 kPa (500 mbar) of nominal connection sizes up to and including DN 150 for use on burners or in appliances using gases such as natural gas, manufactured gas or liquefied petroleum gas (LPG). It is not applicable to corrosive and waste gases. An MFC consists of two or more functions, at least one of which is a mechanical control, as specified in the relevant control standards. This document is also applicable to construction and performance requirements for components of burner ignition systems as specified in Annex K. The requirements and test methods in Annex K include optional type testing and evaluation of these components. This document is applicable to: — water-operated gas valves (see Annex I); — overheating safety devices (OSDs) (see Annex J); and — optional requirements for components of burner control systems (see Annex K).

Dispositifs de commande et de sécurité pour les brûleurs et les appareils à gaz — Exigences particulières — Partie 8: Equipements multifonctionnels

General Information

• Status: Published
• Publication Date: 10-May-2023
• ICS: 27.060.20 - Gas fuel burners
• Technical Committee: ISO/TC 161 - Controls and protective devices for gas and/or oil
• Drafting Committee: ISO/TC 161 - Controls and protective devices for gas and/or oil
• Current Stage: 6060 - International Standard published
• Start Date: 11-May-2023
• Due Date: 06-Aug-2023
• Completion Date: 11-May-2023

Relations

• Revises: ISO 23551-8:2016 - Safety and control devices for gas burners and gas-burning appliances — Particular requirements — Part 8: Multifunctional controls
• Effective Date: 06-Jun-2022
• Revises: ISO 23551-8:2016/Amd 1:2019 - Safety and control devices for gas burners and gas-burning appliances — Particular requirements — Part 8: Multifunctional controls — Amendment 1: Overheating safety devices
• Effective Date: 06-Jun-2022

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 23551-8
Second edition
2023-05
Safety and control devices for gas
burners and gas-burning appliances —
Particular requirements —
Part 8:
Multifunctional controls
Dispositifs de commande et de sécurité pour les brûleurs et les
appareils à gaz — Exigences particulières —
Partie 8: Equipements multifonctionnels
Reference number
ISO 23551-8:2023(E)
© ISO 2023

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ISO 23551-8:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
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ISO 23551-8:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 General terms . 2
3.2 Definitions pertaining to component parts of burner control systems . 3
4 Classes of control . 4
4.1 Classes of controls . 4
4.2 Groups of controls . 4
5 Test conditions .4
6 Construction . 5
6.1 General . 5
6.2 MFC based on combination of controls . 5
6.2.1 General . 5
6.2.2 Interaction between controls . 5
6.3 Components of burner control systems . 6
7 Performance . 6
7.1 Overview . 6
7.2 General . 6
7.3 External leak-tightness of MFC . 6
7.4 Mechanical thermostat function . 6
7.5 Internal leak-tightness of MFC . 6
7.6 Endurance test for combined functions . 6
7.7 Components of burner control systems . 6
8 Electrical equipment . 6
9 Electromagnetic compatibility (EMC) . 7
10 Marking, installation and operating instructions . 7
10.1 Marking . 7
10.2 Installation and operating instructions . 7
10.3 Warning notice . 7
Annex A (informative) Leak-tightness test — Volumetric method . 8
Annex B (informative) Leak-tightness test — pressure-loss method . 9
Annex C (informative) Conversion of pressure loss into leakage rate .10
Annex D (normative) Gas quick connector (GQC).11
Annex E (normative) Elastomers/requirements resistance to lubricants and gas .12
Annex F (normative) Specific regional requirements in European countries.13
Annex G (normative) Specific regional requirements in Canada and the USA .14
Annex H (normative) Specific regional requirements in Japan .15
Annex I (normative) Water-operated gas valves .16
Annex J (normative) Overheating safety devices .18
Annex K (normative) Requirements for components of burner control systems .21
Bibliography .31
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ISO 23551-8:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at  www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 161, Controls and protective devices for
gaseous and liquid fuels.
This second edition cancels and replaces the first edition (ISO 23551-8:2016), which has been technically
revised. It also incorporates the Amendment ISO 23551-8:2016/Amd. 1:2019.
The main changes are as follows:
— the document has been updated to align technically and with the revised format of ISO 23550:2018;
— the document has been updated to align technically and with the relevant latest editions of ISO 23551
series, referenced herein;
— specific regional requirements have been moved from annexes into the main body of the document.
A list of all parts in the ISO 23551 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 23551-8:2023(E)
Introduction
This document is designed to be used in combination with ISO 23550 and relevant parts of the
ISO 23551 series. Together with both ISO 23550 and the ISO 23551 series, this document establishes the
full requirements as they apply to the product covered by this document.
Where needed, this document adapts ISO 23550 by stating the corresponding clause number and
adding:
— “with the following modification”;
— “with the following addition”;
— “is replaced by the following”; or
— “is not applicable”.
In order to identify specific requirements that are particular to this document, that are not already
covered by ISO 23550, this document contains certain clauses or subclauses that are additional to the
structure of ISO 23550. These subclauses are indicated by the introductory sentence: “Subclause (or
Annex) specific to this document."
To ensure global relevance of this document, the differing requirements resulting from practical
experience and installation practices in various regions of the world have been taken into account.
The variations in basic infrastructure associated with gas controls and appliances have also been
recognized, some of which are addressed in Annexes F, G and H. This document intends to provide a
basic framework of requirements that recognize these differences.
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INTERNATIONAL STANDARD ISO 23551-8:2023(E)
Safety and control devices for gas burners and gas-burning
appliances — Particular requirements —
Part 8:
Multifunctional controls
1 Scope
This document specifies safety, construction, performance and testing requirements of multifunctional
controls (MFC) intended for use with gas burners, gas appliances and appliances of similar use.
This document applies to an MFC with declared maximum inlet pressures up to and including 50 kPa
(500 mbar) of nominal connection sizes up to and including DN 150 for use on burners or in appliances
using gases such as natural gas, manufactured gas or liquefied petroleum gas (LPG). It is not applicable
to corrosive and waste gases.
An MFC consists of two or more functions, at least one of which is a mechanical control, as specified in
the relevant control standards.
This document is also applicable to construction and performance requirements for components of
burner ignition systems as specified in Annex K. The requirements and test methods in Annex K include
optional type testing and evaluation of these components.
This document is applicable to:
— water-operated gas valves (see Annex I);
— overheating safety devices (OSDs) (see Annex J); and
— optional requirements for components of burner control systems (see Annex K).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 23550:2018, Safety and control devices for gas and/or oil burners and appliances — General
requirements
ISO 23551-1, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 1: Automatic and semi-automatic shut-off valves
ISO 23551-2, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 2: Pressure regulators
ISO 23551-4, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 4: Valve-proving systems for automatic shut-off valves
ISO 23551-5, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 5: Manual gas valves
ISO 23551-6, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 6: Thermoelectric flame supervision controls
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ISO 23551-8:2023(E)
ISO 23551-9, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 9: Mechanical gas thermostats
ISO 23551-10, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 10: Vent valves
IEC 60730-1:2020, Automatic electrical controls — Part 1: General requirements
IEC 60730-2-5, Automatic electrical controls — Part 2-5: Particular requirements for automatic electrical
burner control systems
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 23550 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 General terms
3.1.1
multifunctional control
MFC
combination of two or more controls, at least one of which is a mechanical control, whereby the
functional parts cannot operate if separated
3.1.2
closing mechanism
part of the actuating mechanism that operates the closure member to the closed position guaranteeing
the gas shut-off function with the required tightness
3.1.3
water operated gas valve
device that uses flow of water to control the flow of gas
3.1.4
overheating safety device
OSD
temperature-sensing device which is intended to keep temperature below one particular value during
abnormal operating conditions of the appliance and which has no provision for setting by the end user
Note 1 to entry: These devices usually use a thermistor or a bimetal sensing part (element).
3.1.5
OSD sensor
part of the overheating safety device control which is intended to be exposed to the influences of the
activating quantity to which the automatic action of a sensing control responds
Note 1 to entry: Examples of OSDs are shown in Figure 1.
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ISO 23551-8:2023(E)
a) Example a) b) Example b)
Key
1 thermo-electric flame supervision control 4 OSD sensor
2 burner 5 object to be measured (heated by burner)
3 gas shut-off valve 6 burner control unit
Figure 1 — Examples of OSDs
3.1.6
overheating temperature
temperature at which the OSD functions to turn off the gas supply to the burner during abnormal
operating conditions of the appliance
3.1.7
thermistor
thermally sensitive semiconductor resistor, which shows over at least part of its resistance/temperature
(R/T) characteristic a significant non-linear change in its electrical resistance with a change in
temperature
[SOURCE: IEC 60730-1:2020, J.2.15.1]
3.1.8
bimetal
object that is composed of two separate metals joined together
3.2 Definitions pertaining to component parts of burner control systems
3.2.1
pilot burner
burner which provides a flame to ignite a main burner(s)
Note 1 to entry: Herein after referred to as a pilot.
3.2.2
sensing element temperature limit
temperature below which the sensing element will act to shut off the fuel supply
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ISO 23551-8:2023(E)
3.2.3
intermittent/continuous ignition
type of ignition which is ignited or energized upon equipment user initiation of the operational cycle
and which remains continuously ignited or energized during the operational cycle then extinguished or
de-energized when the operational cycle is completed
Note 1 to entry: In this type of system, the main burner can cycle on and off multiple times during the complete
equipment use cycle, but the intermittent pilot remains continuously ignited throughout the full cycle even when
the main burner is extinguished.
EXAMPLE A clothes dryer.
3.2.4
intermittent/interrupted ignition
type of ignition which is ignited or energized upon equipment user initiation of the operational cycle
and which is extinguished or de-energized after the equipment use cycle has been initiated
EXAMPLE An example a gas range top or oven burner ignition operation.
3.2.5
oxygen depletion safety shutoff system
ODS
system designed to shut off the main burner and pilot gas to the equipment when the oxygen content of
the room in which the equipment is installed is reduced below a predetermined level
3.2.6
thermocouple
flame sensing device consisting of two dissimilar metal wires joined at one end so that when heat is
applied to the joined end, an electrical junction is formed that generates electrical energy and when the
heat is removed the voltage will decay over time
3.27
fast-acting thermocouple
flame-sensing thermoelectric generating device whose voltage output decays more rapidly than a
common thermocouple
Note 1 to entry: In applications where these devices are used the decay rate does not exceed 30 s.
4 Classes of control
4.1 Classes of controls
Shall be according to ISO 23550:2018, 4.1, and the relevant specific part of the ISO 23551 series as
defined in 6.2.1.
4.2 Groups of controls
Shall be according to ISO 23550:2018, 4.2, and the relevant specific part of the ISO 23551 series as
defined in 6.2.1.
5 Test conditions
Shall be according to ISO 23550:2018, Clause 5.
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ISO 23551-8:2023(E)
6 Construction
6.1 General
ISO 23550:2018, Clause 6, is replaced by the following.
Subclauses specific to this document.
An MFC shall consist of a combination of controls according to 6.2.
Requirements for construction of the controls incorporated in the MFC are covered in the relevant
control standards. Where no control standard is available, the requirements of ISO 23550 are applicable.
In addition, this document covers requirements for the safety-related interactions between the different
functions of the MFC (see 6.2.2).
Where there are no requirements for these interactions between two or more controls, a risk assessment
shall be performed. MFCs shall be designed such that access to internal parts requires the use of tools.
6.2 MFC based on combination of controls
6.2.1 General
MFCs are based on a combination of the functionality provided by the controls as given by the following
list:
— automatic shut-off valves according to ISO 23551-1;
— pressure regulators according to ISO 23551-2;
— valve proving systems according to ISO 23551-4;
— manual gas valves according to ISO 23551-5;
— thermo electric flame supervision devices according to ISO 23551-6;
— mechanical gas thermostats according to ISO 23551-9;
— vent valves according to ISO 23551-10;
— electronic fuel/air ratio controls according to ISO 23552-1;
— automatic electrical burner control system according to IEC 60730-2-5;
— water-operated gas valves according to Annex I.
— OSDs (see Annex J).
6.2.2 Interaction between controls
6.2.2.1 Closing mechanism for closure member
Each automatic shut-off valve shall consist of a separate, independent closing mechanism controlling
only one closure member. A check of internal leak-tightness shall be possible on each of the automatic
shut-off valves. If two or more closure members are controlled by one closing mechanism, the valve is
considered as one automatic shut-off valve.
6.2.2.2 Interactions between functions
The interactions between the functions of the MFC shall not interfere with the safety of the individual
functions. Mechanical functions shall not affect the safety of electronic functions and vice versa.
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ISO 23551-8:2023(E)
6.3 Components of burner control systems
When specified by the manufacturer, components of burner control systems shall meet the construction
requirements specified in Annex K.
7 Performance
7.1 Overview
ISO 23550:2018, Clause 7, is replaced by the following subclauses.
Subclauses specific to this document.
7.2 General
Requirements for performance of MFCs are covered in the relevant control standards (see list in 6.2.1).
Where no control standard is available, the requirements of ISO 23550 are applicable.
7.3 External leak-tightness of MFC
An MFC shall be leak-tight in accordance with the leakage rate given in Table 1. The test is performed
according to ISO 23550:2018, 7.2.2.1 and 7.2.2.2.
Table 1 — External leakage rate
Nominal inlet size External leakage rates
3
DN cm /h of air
DN < 10 60
10 ≤ DN 120
7.4 Mechanical thermostat function
If the MFC incorporates an independent mechanical thermostat function and a pressure regulator, the
pressure regulator shall be put out of action for the tests of the thermostat function.
7.5 Internal leak-tightness of MFC
The leak-tightness of the closure member(s) of each function shall be tested independently.
7.6 Endurance test for combined functions
For an MFC which uses a single closure member to perform more than one function, the test conditions
and number of cycles for endurance testing shall be applied by the function having the most severe
combination.
7.7 Components of burner control systems
When specified by the manufacturer, components of burner control systems shall meet the performance
requirements specified in Annex K.
8 Electrical equipment
Shall be according to ISO 23550:2018, Clause 8.
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ISO 23551-8:2023(E)
9 Electromagnetic compatibility (EMC)
Shall be according to ISO 23550:2018, Clause 9.
10 Marking, installation and operating instructions
10.1 Marking
ISO 23550:2018, 10.1, is replaced by the following.
The marking of MFCs are covered in the relevant control standards as listed under 6.1 and 6.2.1.
10.2 Installation and operating instructions
Shall be according to ISO 23550:2018, 10.2, with the following addition.
Instructions for MFC are covered in the relevant control standards as listed under 6.2.1.
They shall include all of the information of the relevant control standard concerning use, installation,
operation and servicing. They shall also include information on the following points:
a) gas, and if applicable, water connection(s);
b) a statement to the effect that the functions of the MFC have to be verified as being suitable for their
application;
c) if applicable, maximum water pressure (see I.2);
d) if applicable, water flow to open and to close the water operated gas valve.
10.3 Warning notice
Shall be according to ISO 23550:2018, 10.3.
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ISO 23551-8:2023(E)
Annex A
(informative)

Leak-tightness test — Volumetric method
Shall be according to ISO 23550:2018, Annex A.
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ISO 23551-8:2023(E)
Annex B
(informative)

Leak-tightness test — pressure-loss method
Shall be according to ISO 23550:2018, Annex B.
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ISO 23551-8:2023(E)
Annex C
(informative)

Conversion of pressure loss into leakage rate
Shall be according to ISO 23550:2018, Annex C.
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ISO 23551-8:2023(E)
Annex D
(normative)

Gas quick connector (GQC)
Shall be according to ISO 23550:2018, Annex D.
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ISO 23551-8:2023(E)
Annex E
(normative)

Elastomers/requirements resistance to lubricants and gas
Shall be according to ISO 23550:2018, Annex E.
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ISO 23551-8:2023(E)
Annex F
(normative)

Specific regional requirements in European countries
Shall be according to ISO 23550:2018, Annex F.
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ISO 23551-8:2023(E)
Annex G
(normative)

Specific regional requirements in Canada and the USA
Shall be according to ISO 23550:2018, Annex G.
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ISO 23551-8:2023(E)
Annex H
(normative)

Specific regional requirements in Japan
Shall be according to ISO 23550:2018, Annex H.
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ISO 23551-8:2023(E)
Annex I
(normative)

Water-operated gas valves
I.1 General
Annex specific to this document. This annex is applicable to the specific requirements of an MFC that
incorporates a water-operated gas valve function. An MFC that incorporates a water-operated gas valve
shall conform to the additional requirements given under I.2.
I.2 Additional requirements
I.2.1 Construction
In addition to the provisions of 6.1, the following applies.
The water-operated gas valve shall subordinate the admission of gas to the gas outlet to the water flow
through it.
In the event of leakage at the joint sealing of the water circuit, it shall not be possible for water to
penetrate into the gas circuit. To this end, there shall be a space between the gas-carrying and water-
carrying parts of the water-operated gas valve. This space shall provide drainage with an opening
2
having an area of at least 19 mm . It may consist of one or more orifices of which the smallest transverse
dimension shall not
...

DRAFT INTERNATIONAL STANDARD
ISO/DIS 23551-8
ISO/TC 161 Secretariat: DIN
Voting begins on: Voting terminates on:
2022-04-27 2022-07-20
Safety and control devices for gas burners and gas-burning
appliances — Particular requirements —
Part 8:
Multifunctional controls
Dispositifs de commande et de sécurité pour les brûleurs et les appareils à gaz — Exigences particulières —
Partie 8: Equipements multifonctionnels
ICS: 27.060.20
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
This document is circulated as received from the committee secretariat.
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 23551-8:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022

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ISO/DIS 23551-8:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
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ISO/DIS 23551-8:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Classes of control . 4
4.1 Classes of controls . 4
4.2 Groups of controls . 4
5 Test conditions .4
6 Construction . 5
6.1 General . 5
6.2 MFC based on combination of controls . 5
6.2.1 General . 5
6.2.2 Interaction between Controls . 5
7 Performance . 6
7.1 General . 6
7.2 External leak-tightness of MFC . 6
7.3 Mechanical thermostat function . 6
7.4 Internal leak tightness of MFC . . 6
7.5 Endurance test for combined functions . 6
7.6 Components of burner control systems . 6
8 Electrical equipment . 7
9 Electromagnetic compatibility (EMC) . 7
10 Marking, installation and operating instructions . 7
10.1 Marking . 7
10.2 Installation and operating instructions . 7
10.3 Warning notice . 7
Annex A (informative) Leak-tightness test — Volumetric method . 8
Annex B (informative) Leak-tightness test — pressure-loss method . 9
Annex C (informative) Conversion of pressure loss into leakage rate .10
Annex D (normative) Gas quick connector (GQC) .11
Annex E (normative) Elastomers/requirements resistance to lubricants and gas .12
Annex F (normative) Specific regional requirements in European countries .13
Annex G (normative) Specific regional requirements in Canada and the USA .14
Annex H (normative) Specific regional requirements in Japan .15
Annex I (normative) Water operated gas valves .16
Annex J (normative) Overheating safety devices .18
Annex K (normative) Requirements for Components of Burner Control Systems .21
Bibliography .31
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ISO/DIS 23551-8:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 161, Control and protective devices for gas
and/or oil burners and appliances.
This second edition cancels and replaces the first edition (ISO 23551-8:2016), which has been technically
revised.
The main changes compared to the previous edition are as follows:
a) Updated to align technically and with the revised format of the latest edition of ISO 23550, General
requirements.
b) Updated to align technically and with the relevant latest editions of ISO 23551 series, referenced
herein.
c) Relocation of specific regional requirements into the main body of the standard that were
previously contained in regional Annexes.
d) Incorporation of amendment ISO 23551-8:2016/Amd 1:2019 and draft ISO 23551-8:2016/DAmd 2.
A list of all parts in the ISO 23551 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/DIS 23551-8:2022(E)
Introduction
This document is designed to be used in combination with ISO 23550 and relevant parts of the ISO
Series 23551. Together with both ISO 23550 and 23551, this document establishes the full requirements
as they apply to the product covered by this
Where needed, this document adapts ISO 23550 by stating in the corresponding clause:
— “with the following modification”;
— “with the following addition”;
— “is replaced by the following”; or
— “is not applicable”.
In order to identify specific requirements that are particular to this document, that are not already
covered by ISO 23550, this document can contain clauses or subclauses that are additional to the
structure of ISO 23550. These subclauses are indicated by the introductory sentence: “Subclause (or
Annex) specific to this document.I
To ensure global relevance of this document, the differing requirements resulting from practical
experience and installation practices in various regions of the world have been taken into account.
The variations in basic infrastructure associated with gas controls and appliances have also been
recognized, some of which are addressed in Annexes F, G and H. This document intends to provide a
basic framework of requirements that recognize these differences
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DRAFT INTERNATIONAL STANDARD ISO/DIS 23551-8:2022(E)
Safety and control devices for gas burners and gas-burning
appliances — Particular requirements —
Part 8:
Multifunctional controls
1 Scope
This document specifies safety, constructional and performance and testing requirements of
multifunctional controls intended for use with gas burners, gas appliances and appliances of similar
use, hereafter referred to as “MFC”.
This document applies to an MFC with declared maximum inlet pressures up to and including 50 kPa
(500 mbar) of nominal connection sizes up to and including DN 150 for use on burners or in appliances
using gases such as natural gas, manufactured gas or liquefied petroleum gas (LPG). It is not applicable
to corrosive and waste gases.
An MFC consists of two or more functions, at least one of which is a mechanical control, as specified in
the relevant control standards.
This document is also applicable to construction and performance requirements for components
of burner ignition systems as specified in Annex K. The requirements and test methods in Annex K
includes optional type testing and evaluation of these components.
This document is applicable to
— water operated gas valves (see Annex I),
— OSDs (see Annex J) and
— Optional Requirements for Components of Burner Control Systems (see Annex K).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 23550:2018, Safety and control devices for gas burners and gas-burning appliances — General
requirements
ISO 23551-1, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 1: Automatic and semi-automatic valves
ISO 23551-2, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 2: Pressure regulators
ISO 23551-4, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 4: Valve-proving systems for automatic shut-off valves
ISO 23551-5, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 5: Manual gas valves
ISO 23551-6, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 6: Thermoelectric flame supervision controls
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ISO/DIS 23551-8:2022(E)
ISO 23551-9, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 9: Mechanical gas thermostats
ISO 23551-10, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 10: Vent valves
ISO 23552-1, Safety and control devices for gas and/or oil burners and gas and/or oil appliances —
Particular requirements — Part 1: Fuel/air ratio controls, electronic type
IEC 60730-2-5, Automatic electrical controls — Part 2-5: Particular requirements for automatic electrical
burner control systems
3 Terms and definitions
For the purpose of this document, the terms and definitions given in ISO 23550and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
multifunctional control
combination of two or more controls, at least one of this is a mechanical control, whereby the functional
parts cannot operate if separated
3.2
closing mechanism
part of the actuating mechanism that operates the closure member to the closed position guaranteeing
the gas shut-off function with the required tightness
3.3
water operated gas valve
device that uses flow of water to control the flow of gas
3.4
overheating safety device
OSD
temperature-sensing device which is intended to keep temperature below one particular value during
abnormal operating conditions of the appliance and which has no provision for setting by the end user
Note 1 to entry: These devices usually use a thermistor or a bimetal sensing part (element).
3.5
sensing part
part of the OSD which is intended to be exposed to the influences of the activating quantity to which the
automatic action of a sensing control responds
Note 1 to entry: Examples of OSDs are shown in Figure 1.
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ISO/DIS 23551-8:2022(E)
Example a) Example b)
Key
1 thermo-electric flame supervision control 4 sensor
2 burner 5 object to be measured (heated by burner)
3 gas shut-off valve 6 burner control unit
Figure 1 — Examples of OSDs
3.6
overheating temperature
temperature at which the OSD functions to turn off the gas supply to the burner during abnormal
operating conditions of the appliance
3.7
thermistor
thermally sensitive semiconductor resistor, which shows over at least part of its resistance/temperature
(R/T) characteristic a significant non-linear change in its electrical resistance with a change in
temperature
[SOURCE: IEC 60730-1, Ed. 5.2:2020, J.2.15.1]
3.8
bimetal
object that is composed of two separate metals joined together
3.9 Definitions pertaining to component parts of burner control systems
3.9.1
pilot burner
burner which provides a flame to ignite a main burner(s)
Note 1 to entry: Herein after referred to as a pilot.
3.9.2
sensing element temperature limit
temperature below which the sensing element will act to shut off the fuel supply
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ISO/DIS 23551-8:2022(E)
3.9.3
intermittent/continuous ignition
type of ignition which is ignited or energized upon equipment user initiation of the operational cycle
and which remains continuously ignited or energized during the operational cycle then extinguished or
de-energized when the operational cycle is completed
Note 1 to entry: In this type of system, the main burner may cycle on and off multiple times during the complete
equipment use cycle, but the intermittent pilot remains continuously ignited throughout the full cycle even when
the main burner is extinguished. An example would be a clothes dryer.
3.9.4
intermittent/interrupted ignition
type of ignition which is ignited or energized upon equipment user initiation of the operational cycle
and which is extinguished or de-energized after the equipment use cycle has been initiated
Note 1 to entry: An example would be a gas range top or oven burner ignition operation.
3.9.5
oxygen depletion safety shutoff system
ODS
system designed to shut off the main burner and pilot gas to the equipment when the oxygen content of
the room in which the equipment is installed is reduced below a predetermined level
3.9.6
millivoltage circuit
circuit which receives its electrical energy by means of a thermocouple(s) or photovoltaic device(s)
3.9.7
thermocouple
flame sensing device consisting of two dissimilar metal wires joined at one end so that when heat is
applied to the joined end form an electrical junction that generates electrical energy and when the heat
is removed the voltage will decay over time
3.9.8
fast acting thermocouple
flame sensing thermoelectric generating device whose voltage output decays more rapidly than a
common thermocouple
Note 1 to entry: In applications where these devices are used the decay rate does not exceed 30 s.
3.9.9
flame failure lock-out time
period of time between the signal indicating absence of flame and lock-out
[SOURCE: IEC 60730-2-5, Ed. 4.2:2021, 2.3.107]
4 Classes of control
4.1 Classes of controls
Shall be according to ISO 23550:2018 and relevant 23551, 4.1.
4.2 Groups of controls
Shall be according to ISO 23550:2018 and relevant 23551, 4.2.
5 Test conditions
Shall be according to ISO 23550:2018, Clause 5.
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ISO/DIS 23551-8:2022(E)
6 Construction
ISO 23550:2018, Clause 6 is replaced by the following.
Subclauses specific to this document.
6.1 General
An MFC consists of a combination of controls according to 6.2.
Requirements for construction of the controls incorporated in the MFC are covered in the relevant
control standards. Where no control standard is available, the requirements of ISO 23550:2018 are
applicable.
In addition, this part of ISO 23551 covers in 6.2.2 requirements for the safety related interactions
between the different functions of the MFC.
Where there are no requirements for these interactions between two or more controls, a risk assessment
shall be performed. MFCs shall be designed such that access to internal parts requires the use of tools.
6.2 MFC based on combination of controls
6.2.1 General
MFC’s are based on a combination of the functionality provided by the controls as given by the following
list:
— automatic shut-off valves according to ISO 23551-1;
— pressure regulators according to ISO 23551-2;
— valve proving systems according to ISO 23551-4;
— manual gas valves according to ISO 23551-5;
— thermo electric flame supervision devices according to ISO 23551-6;
— mechanical gas thermostats according to ISO 23551-9;
— vent valves according to ISO 23551-10;
— electronic fuel/air ratio controls according to ISO 23552-1;
— automatic electrical burner control system according to IEC 60730-2-5;
— water operated gas valves according to Annex II.
— OSDs (see Annex J).
6.2.2 Interaction between Controls
6.2.2.1 Closing mechanism for closure member
Each automatic shut-off valve shall consist of a separate, independent closing mechanism controlling
only one closure member. A check of internal leak-tightness shall be possible on each of the automatic
shut-off valves. If two or more closure members are controlled by one closing mechanism, the valve is
considered as one automatic shut-off valve.
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ISO/DIS 23551-8:2022(E)
6.2.2.2 Interactions between functions
The interactions between the functions of the MFC shall not interfere with the safety of the individual
functions. Mechanical functions shall not affect the safety of electronic functions and vice versa.
6.3 Components of burner control systems
When specified by the manufacturer, components of burner control systems shall meet the construction
requirements specified in Annex K.
7 Performance
ISO 23550:2018, Clause 7 is replaced by the following.
Subclauses specific to this document.
7.1 General
Requirements for performance of MFC’s are covered in the relevant control standards (see list in 6.2.1).
Where no control standard is available, the requirements of ISO 23550:2018 are applicable.
7.2 External leak-tightness of MFC
An MFC shall be leak-tight in accordance with the leakage rate given in Table 1. The test is performed
according to ISO 23550:2018, 7.2.2.1 and 7.2.2.2.
Table 1 — External leakage rate
Nominal inlet size External leakage rates
3
DN cm /h of air
DN < 10 60
10 ≤ DN 120
7.3 Mechanical thermostat function
If the MFC incorporates an independent mechanical thermostat function and a pressure regulator, the
pressure regulator shall be put out of action for the tests of the thermostat function.
7.4 Internal leak tightness of MFC
The leak-tightness of the closure member(s) of each function shall be tested independently.
7.5 Endurance test for combined functions
For MFC which uses a single closure member to perform more than one function, the test conditions
and number of cycles for endurance testing shall be applied by the function having the most severe
combination.
7.6 Components of burner control systems
When specified by the manufacturer, components of burner control systems shall meet the performance
requirements specified in Annex K.
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ISO/DIS 23551-8:2022(E)
8 Electrical equipment
Shall be according to ISO 23550:2018, Clause 8.
9 Electromagnetic compatibility (EMC)
Shall be according to ISO 23550:2018, Clause 9.
10 Marking, installation and operating instructions
10.1 Marking
ISO 23550:2018, 10.1 is replaced by the following.
Marking of MFC are covered in the relevant control standards as listed under 6.1 and 6.2.1.
10.2 Installation and operating instructions
Shall be according to ISO 23550:2018, 10.2 with the following addition.
Instructions of MFC are covered in the relevant control standards as listed under 6.2.1.
They shall include all the information of the relevant control standard on use, installation, operation
and servicing. Furthermore, they shall also include the following:
a) gas, and if applicable, water connection(s);
b) a statement to the effect that the functions of the MFC have to be verified as being suitable for their
application;
c) if applicable, maximum water pressure (see I.2);
d) if applicable, water flow to open and to close the water operated gas valve;
10.3 Warning notice
Shall be according to ISO 23550:2018, 10.3.
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ISO/DIS 23551-8:2022(E)
Annex A
(informative)

Leak-tightness test — Volumetric method
Shall be according to ISO 23550:2018, Annex A.
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ISO/DIS 23551-8:2022(E)
Annex B
(informative)

Leak-tightness test — pressure-loss method
Shall be according to ISO 23550:2018, Annex B.
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ISO/DIS 23551-8:2022(E)
Annex C
(informative)

Conversion of pressure loss into leakage rate
Shall be according to ISO 23550:2018, Annex C.
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ISO/DIS 23551-8:2022(E)
Annex D
(normative)

Gas quick connector (GQC)
Shall be according to ISO 23550:2018, Annex D.
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ISO/DIS 23551-8:2022(E)
Annex E
(normative)

Elastomers/requirements resistance to lubricants and gas
Shall be according to ISO 23550:2018, Annex E.
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ISO/DIS 23551-8:2022(E)
Annex F
(normative)

Specific regional requirements in European countries
Shall be according to ISO 23550:2018, Annex F.
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ISO/DIS 23551-8:2022(E)
Annex G
(normative)

Specific regional requirements in Canada and the USA
Shall be according to ISO 23550:2018, Annex G.
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ISO/DIS 23551-8:2022(E)
Annex H
(normative)

Specific regional requirements in Japan
Shall be according to ISO 23550:2018, Annex H.
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ISO/DIS 23551-8:2022(E)
Annex I
(normative)

Water operated gas valves
Annex specific to this document.
I.1 General
This Annex is applicable to the specific requirements of an MFC that incorporates a water operated
gas valve function. MFC that incorporates a water operated gas valve shall comply with the additional
requirements given under I.2.
Only the affected subclauses are mentioned in this Annex, hence, the numbering is non-consecutive.
I.2 Additional requirements
I.6.1  Construction
The water operated gas valve shall subordinate the admission of gas to the gas outlet to the water flow
through it.
In the event of leakage at the joint sealing of the water circuit, it shall not be possible for water to
penetrate into the gas circuit. To this end, there shall be a space between the gas carrying and water
...