Mechanical thermostats for gas-burning appliances

EN 13611:2019, Clause 1 applies with the following modification and addition:
Modification:
The 1st paragraph of EN 13611:2019, Clause 1 is replaced by:
This document specifies the safety, design, construction, and performance requirements and testing for mechanical thermostats intended for use with gas appliances and similar use, hereafter referred to as “thermostats”.
This document is applicable to thermostats with declared maximum inlet pressures up to and including 50 kPa and of nominal connection sizes up to and including DN 50 for use with one or more fuel gases.
Addition:
This document is applicable to thermostats controlling the gas flow directly or indirectly through an integral gas valve. This document applies to thermostats used with gas appliances which are not installed in the open air.
Thermostats dealt with in this document are intended for control functions.
This document is not applicable to:
a)   controls which use auxiliary energy (e.g. electrical energy supplied externally);
b)   an assessment of the control regarding Performance Level (PL) and Safety Integrity Level (SIL).
The 4th paragraph of EN 13611:2019, Clause 1 is removed.

Mechanische Temperaturregler für Gasgeräte

Dieses Dokument legt die Anforderungen an die Sicherheit, konstruktive Ausführung und Funktion von mechanischen Temperaturreglern fest, im Folgenden als „Temperaturregler“ bezeichnet, die für die Verwendung mit Gasgeräten und ähnliche Verwendungszwecke vorgesehen sind.
Dieses Dokument gilt für Temperaturregler mit Nenn-Anschlussmaßen bis einschließlich DN 50 mit einem höchsten angegebenen Eingangsdruck bis einschließlich 50 kPa (500 mbar) für die Verwendung mit einem oder mehreren Brenngasen nach EN 437.
Dieses Dokument gilt für Temperaturregler, die den Gasstrom direkt oder indirekt durch ein eingebautes Gasventil steuern.
Dieses Dokument gilt nur für Temperaturregler, die in Gasgeräten verwendet werden, die nicht im Freien aufgestellt sind.
Die in diesem Dokument behandelten Temperaturregler sind für Regel- und Steuerfunktionen vorgesehen.
Dieses Dokument ist nicht anwendbar auf:
a)   das Thermoelement;
b)    Regel- und Steuergeräte, die Hilfsenergie nutzen (z. B. von außen zugeführte elektrische Energie);
c)   eine Bewertung der Regeleinrichtung in Bezug auf Performance Level (PL) und Sicherheits-Integritätslevel (SIL).

Thermostats mécaniques pour appareils à gaz

L’article 1 de la norme EN13611 :2019 s’applique avec la modification et l’addition suivantes :
Modification :
Le 1er paragraphe de l’article 1 de la norme EN 13611:2019 est remplacé par ce qui suit :
Le présent document spécifie les caractéristiques de sécurité, de construction et de fonctionnement ainsi que les essais applicables aux thermostats mécaniques équipant les appareils utilisant des combustibles gazeux et d'utilisation similaire, ci-après désignés « thermostats ».
Ce document s'applique aux thermostats de pression amont maximale déclarée inférieure ou égale à 50 kPa , de diamètre nominal de raccordement inférieur ou égal à DN 50 et utilisés avec un ou plusieurs combustibles gazeux.
Addition :
Ce document est applicable aux thermostats qui contrôlent le débit du gaz directement ou indirectement au moyen d'une vanne de gaz intégrée.  Il s'applique seulement aux thermostats utilisés sur des appareils utilisant des combustibles gazeux qui ne sont pas installés en plein air.
Les thermostats visés par le présent document assurent des fonctions de régulation.
Ce document ne s'applique pas :
a)   aux équipements utilisant une énergie auxiliaire (par exemple, alimentation en énergie électrique externe) ;
b)   à une évaluation du niveau de performance (PL) et du niveau d'intégrité de sécurité (SIL) de l'équipement.
Le 4ième paragraphe de l’article 1 de la EN 13611 :2019 est supprimé.

Mehanski termostati za plinske aparate

General Information

Status
Published
Publication Date
11-Oct-2022
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Start Date
12-Oct-2022
Due Date
02-Feb-2022
Completion Date
12-Oct-2022

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SLOVENSKI STANDARD
SIST EN 257:2022
01-december-2022
Nadomešča:
SIST EN 257:2010
Mehanski termostati za plinske aparate
Mechanical thermostats for gas-burning appliances
Mechanische Temperaturregler für Gasgeräte
Thermostats mécaniques pour appareils à gaz
Ta slovenski standard je istoveten z: EN 257:2022
ICS:
17.200.20 Instrumenti za merjenje Temperature-measuring
temperature instruments
27.060.20 Plinski gorilniki Gas fuel burners
SIST EN 257:2022 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 257:2022
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SIST EN 257:2022
EN 257
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2022
EUROPÄISCHE NORM
ICS 27.060.20 Supersedes EN 257:2010
English Version
Mechanical thermostats for gas-burning appliances

Thermostats mécaniques pour appareils à gaz Mechanische Temperaturregler für Gasgeräte

This European Standard was approved by CEN on 8 August 2022.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 257:2022 E

worldwide for CEN national Members.
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SIST EN 257:2022
EN 257:2022 (E)
Contents Page

European foreword ....................................................................................................................................................... 4

Introduction .................................................................................................................................................................... 5

1 Scope ............................................................................................................................................................. 7

2 Normative references ............................................................................................................................. 7

3 Terms and definitions ............................................................................................................................ 7

4 Classification .............................................................................................................................................. 9

4.1 Classes of control ...................................................................................................................................... 9

4.2 Groups of control...................................................................................................................................... 9

4.3 Classes of control functions .................................................................................................................. 9

4.4 Types of DC supplied controls .......................................................................................................... 10

5 Test conditions and uncertainty of measurements .................................................................. 10

6 Design and construction ..................................................................................................................... 10

6.1 General ...................................................................................................................................................... 10

6.2 Mechanical parts of the control ....................................................................................................... 10

6.3 Materials................................................................................................................................................... 11

6.4 Gas connections ..................................................................................................................................... 11

6.5 Electrical parts of the control ........................................................................................................... 11

6.6 Protection against internal faults for the purpose of functional safety ............................ 11

6.101 Flow characteristics ............................................................................................................................. 11

6.102 Temperature adjustment ................................................................................................................... 11

7 Performance ........................................................................................................................................... 12

7.1 General ...................................................................................................................................................... 12

7.2 Leak-tightness ........................................................................................................................................ 13

7.3 Torsion and bending ............................................................................................................................ 13

7.4 Rated flow rate ....................................................................................................................................... 13

7.5 Durability ................................................................................................................................................. 14

7.6 Performance tests for electronic controls ................................................................................... 14

7.7 Long-term performance for electronic controls ........................................................................ 14

7.8 Data exchange ........................................................................................................................................ 14

7.101 Calibration temperature set-point ................................................................................................. 14

7.102 Backlash ................................................................................................................................................... 14

7.103 Opening of a snap-acting thermostat with a closed position ................................................ 15

7.104 Opening pressure and closing pressure for thermostats with a closed position .......... 15

7.105 Operating characteristic of the thermostat ................................................................................. 15

7.106 Ambient temperature range of the body ...................................................................................... 19

7.107 Effect of storage and transport temperatures ............................................................................ 19

7.108 Thermal overload of the temperature sensor ............................................................................ 20

7.109 Operating torque of the thermostat set-point adjuster .......................................................... 20

7.110 Endurance ................................................................................................................................................ 20

8 Electrical requirements ...................................................................................................................... 22

9 Electromagnetic compatibility (EMC) ............................................................................................ 22

10 Marking, instructions .......................................................................................................................... 22

10.1 Marking ..................................................................................................................................................... 22

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SIST EN 257:2022
EN 257:2022 (E)

10.2 Instructions.............................................................................................................................................. 22

10.3 Warning notice ....................................................................................................................................... 23

Annex A (informative) Abbreviations and Symbols ...................................................................................... 24

Annex B (informative) Leak-tightness tests for gas controls – volumetric method .......................... 25

Annex C (informative) Leak-tightness tests for gas controls – pressure loss method ...................... 26

Annex D (normative) Conversion of pressure loss into leakage rate ..................................................... 27

Annex E (normative) Electrical/electronic component fault modes ...................................................... 28

Annex F (normative) Additional requirements for safety accessories and pressure

accessories as defined in EU Directive 2014/68/EU ................................................................ 29

Annex G (normative) Materials for pressurized parts ................................................................................. 30

Annex H (normative) Additional materials for pressurized parts .......................................................... 31

Annex I (normative) Requirements for controls used in DC supplied burners and

appliances burning gaseous or liquid fuels ................................................................................. 32

Annex J (normative) Method for the determination of the Safety Integrity Level (SIL) ................... 33

Annex K (normative) Method for the determination of a Performance Level (PL) ........................... 34

Annex L (informative) Relationship between Safety Integrity Level (SIL) and

Performance Level (PL) ....................................................................................................................... 35

Annex M (normative) Reset functions ................................................................................................................ 36

Annex N (informative) Guidance document on Environmental Aspects ............................................... 37

Annex O (normative) Seals of elastomers, cork and synthetic fibre mixtures .................................... 38

Annex ZA (informative) Relationship between this European Standard and the essential

requirements of Regulation (EU) 2016/426 aimed to be covered ...................................... 39

Bibliography ................................................................................................................................................................. 42

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SIST EN 257:2022
EN 257:2022 (E)
European foreword

This document (EN 257:2022) has been prepared by Technical Committee CEN/TC 58 “Safety and

control devices for burners and appliances burning gaseous or liquid fuels”, the secretariat of which is

held by BSI.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by April 2023, and conflicting national standards shall be

withdrawn at the latest by October 2025.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN 257:2010.

The following significant changes compared to the previous edition have been incorporated in this

document:
a) alignment with EN 13611:2019;
b) requirements from EU Directive 2014/68/EU were not adopted;
c) updating of Clause 2, normative references;
d) reference to EN 437 removed;

e) information on life time for safe function (designed lifetime) added to instructions.

This document has been prepared under a Standardization Request given to CEN by the European

Commission and the European Free Trade Association, and supports essential requirements of

EU Directive(s) / Regulation(s).

For relationship with EU Directive(s) / Regulation(s), see informative Annex ZA, which is an integral part

of this document.

Any feedback and questions on this document should be directed to the users’ national standards body.

A complete listing of these bodies can be found on the CEN website.

According to the CEN-CENELEC Internal Regulations, the national standards organisations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,

Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,

Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North

Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the United

Kingdom.
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SIST EN 257:2022
EN 257:2022 (E)
Introduction
This document is intended to be used in conjunction with EN 13611:2019.

EN 13611:2019 recognizes the safety level specified by CEN/TC 58 and is regarded as a horizontal

standard dealing with the safety, construction, performance and testing of controls for burners and

appliances burning gaseous and/or liquid fuels.

The general requirements for controls are given in EN 13611:2019, and methods for classification and

assessment for new controls and control functions are given in EN 14459:2021 (see Figure 1).

EN 126:2012 (see Figure 1) specifies multifunctional controls combining two or more controls and

Application Control Functions, one of which is a mechanical control function. The requirements for

controls and Application Control Functions are given in the specific control standard (see Figure 1,

control functions).
Figure 1 — Interrelation of control standards

EN 13611:2019 should be used in conjunction with the specific standard for a specific type of control (e.g.

EN 88-1:2022, EN 88-2:2022, EN 88-3:2022, EN 125:2022, EN 126:2012, EN 161:2022, EN 257:2022,

EN 298:2022, EN 1106:2022, EN 1643:2022, EN 1854:— , EN 12067-2:2022, EN 16304:2022,

EN 16340:2014, EN 16678:2022 and EN 16898:2022), or for controls for specific applications.

EN 13611:2019 can also be applied, so far as reasonable, to controls not mentioned in a specific standard

and to controls designed on new principles, in which case additional requirements can be necessary.

EN 14459:2021 provides methods for classification and assessment of new control principles.

Primarily in industrial applications it is common practice to rate the safety of a plant based on values

describing the likelihood of a dangerous failure. These values are being used to determine Safety Integrity

Levels or Performance Levels when the system is being assessed in its entirety.

CEN/TC 58 standards for safety relevant controls do go beyond this approach, because for a certain life

time for which the product is specified, designed and tested a dangerous failure is not allowed at all.

Failure modes are described and assessed in greater detail.
Under preparation. Stage at the time of publication: FprEN 1854:2022.
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SIST EN 257:2022
EN 257:2022 (E)

Measures to prevent from dangerous situations are defined. Field experience over many decades is

reflected in the CEN/TC 58 standards. Requirements of EN 13611:2019 can be considered as proven in

practice.

This document refers to clauses of EN 13611:2019 or adapts clauses by stating “with the following

modification”, “with the following addition”, “is replaced by the following” or “is not applicable” in the

corresponding clause.

This document adds clauses or subclauses to the structure of EN 13611:2019 which are particular to this

document. Subclauses which are additional to those in EN 13611:2019 are numbered starting from 101.

Additional Annexes are designated as Annex AA, Annex BB, Annex CC, etc. It should be noted that these

clauses, subclauses and Annexes are not indicated as an addition.

If by reference to EN 13611:2019 the term “control” is given, this term should be read as “thermostat”.

---------------------- Page: 8 ----------------------
SIST EN 257:2022
EN 257:2022 (E)
1 Scope
EN 13611:2019, Clause 1 applies with the following modification and addition:
Modification:
The 1 paragraph of EN 13611:2019, Clause 1 is replaced by:

This document specifies the safety, design, construction, and performance requirements and testing for

mechanical thermostats intended for use with gas appliances and similar use, hereafter referred to as

“thermostats”.

This document is applicable to thermostats with declared maximum inlet pressures up to and including

50 kPa and of nominal connection sizes up to and including DN 50 for use with one or more fuel gases.

Addition:

This document is applicable to thermostats controlling the gas flow directly or indirectly through an

integral gas valve. This document applies to thermostats used with gas appliances which are not installed

in the open air.
Thermostats dealt with in this document are intended for control functions.
This document is not applicable to:

a) controls which use auxiliary energy (e.g. electrical energy supplied externally);

b) an assessment of the control regarding Performance Level (PL) and Safety Integrity Level (SIL).

The 4 paragraph of EN 13611:2019, Clause 1 is removed.
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.

EN 13611:2019 , Safety and control devices for burners and appliances burning gaseous and/or liquid fuels

— General requirements
3 Terms and definitions

For the purposes of this document, the terms and definitions given in EN 13611:2019 and the following

apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.101
mechanical thermostat

thermostat which controls the temperature by adjusting the flow rate accordingly to the temperature of

the sensor without any external energy, such that the temperature remains within defined limits

As impacted by EN 13611:2019/AC:2021.
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SIST EN 257:2022
EN 257:2022 (E)
3.102
adjustable thermostat

mechanical thermostat in which the temperature set-point can be adjusted by the user to anywhere

between minimum and maximum values
3.103
fixed setting thermostat

mechanical thermostat that has a preset fixed operating temperature which cannot be adjusted by the

user
3.104
snap-acting thermostat

mechanical thermostat with only two positions for the flow rate, i.e. “full on-off”, “full on-reduced rate”

or “reduced rate-off”
3.105
modulating thermostat

mechanical thermostat which controls the flow rate in accordance with a predetermined and continuous

function of the temperature of the temperature sensor
3.106
modulating thermostat with additional on-off action

mechanical thermostat which acts as a snap-acting thermostat between the closed and reduced positions

and as a modulating thermostat between the reduced and full-on positions
3.107
thermostat closure member

movable part of the thermostat which opens and closes the gas way and/or varies the flow rate

3.108
presetting device
device for adjusting an operating condition only by an authorized person

Note 1 to entry: It may be fixed or variable, e.g. when it is the gas flow that is adjustable; either an orifice or an

adjusting screw may be used.
3.109
fixed bypass

non-adjustable presetting device for fixing the minimum gas flow through a thermostat

3.110
bypass adjusting device

screw adjustment or an exchangeable orifice, that fixes the minimum gas flow rate through the

thermostat, and which is accessible only by the use of tools
3.111
temperature sensor

device which senses the temperature of the medium to be controlled or to be supervised

3.112
operating curve

graphical representation of the flow rate as a function of the sensor temperature at a given temperature

set-point and at a constant inlet pressure
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SIST EN 257:2022
EN 257:2022 (E)
3.113
backlash

difference of position of the adjusting knob when it is moved in both directions to obtain the same flow

rate at a constant sensor temperature
3.114
adjusting knob
adjustable spindle
part of the thermostat which is used to select the temperature set-point
3.115
temperature set-point

any value selected within the temperature range at which the controlled temperature should be

maintained
3.116
temperature set-point range
range between the minimum and maximum adjustable temperature set-points

Note 1 to entry: The temperature can be adjusted between the set-points by means of the adjusting knob.

3.117
calibration flow rate
flow rate stated in the instructions for calibration
3.118
calibration temperature set-point

temperature at which the calibration flow rate should be obtained with the adjustment set to the position

and in the direction stated in the instructions
3.119
temperature differential for snap-acting thermostats

difference in temperature necessary to obtain a change in the flow rate, at a given set-point

3.120
deviation

maximum deviation from the temperature set-point which is stated in the instructions

3.121
drift
permanent change in the operating curve of the thermostat
4 Classification
4.1 Classes of control
EN 13611:2019, 4.1 is not applicable.
4.2 Groups of control
Shall be according to EN 13611:2019, 4.2.
4.3 Classes of control functions
EN 13611:2019, 4.3 is not applicable.
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SIST EN 257:2022
EN 257:2022 (E)
4.4 Types of DC supplied controls
EN 13611:2019, 4.4 is not applicable.
5 Test conditions and uncertainty of measurements
Shall be according to EN 13611:2019, Clause 5.
6 Design and construction
6.1 General
Shall be according to EN 13611:2019, 6.1 with the following modification:
The 3 paragraph of EN 13611:2019, 6.1 is not applicable.
6.2 Mechanical parts of the control
6.2.1 Appearance
Shall be according to EN 13611:2019, 6.2.1.
6.2.2 Holes
Shall be according to EN 13611:2019, 6.2.2.
6.2.3 Breather holes
Shall be according to EN 13611:2019, 6.2.3.
6.2.4 Screwed fastenings
Shall be according to EN 13611:2019, 6.2.4.
6.2.5 Jointing
Shall be according to EN 13611:2019, 6.2.5.
6.2.6 Moving parts
Shall be according to EN 13611:2019, 6.2.6.
6.2.7 Sealing caps
Shall be according to EN 13611:2019, 6.2.7.
6.2.8 Dismantling and reassembly
Shall be according to EN 13611:2019, 6.2.8 with the following addition:

If, in accordance with the instructions the thermostat can be dismantled for servicing, such action shall

not result in a change in temperature calibration exceeding the stated maximum set-point deviation

(see 7.101.1).
6.2.9 Auxiliary canals and orifices
Shall be according to EN 13611:2019, 6.2.9.
6.2.10 Presetting device
Shall be according to EN 13611:2019, 6.2.10.
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SIST EN 257:2022
EN 257:2022 (E)
6.3 Materials
Shall be according to EN 13611:2019, 6.3.
6.4 Gas connections
Shall be according to EN 13611:2019, 6.4.
6.5 Electrical parts of the control
EN 13611:2019, 6.5 is not applicable.
6.6 Protection against internal faults for the purpose of functional safety
EN 13611:2019, 6.6 is not applicable.
6.101 Flow characteristics

An adjustable bypass shall be set by means of a variable presetting device or shall be adjusted by means

of a fixed presetting device.

It shall be possible to gain access to any fixed bypass or bypass adjusting device for cleaning without

changing the calibration temperature set-point.

The opening and closing of the thermostat closure member with a total shut-off function shall happen by

snap-action between the off position and the reduced flow position.

NOTE Figure 3 shows typical operating curves of a modulating, snap-acting and modulating on-off thermostat.

The flow rate at the moment of snap-action shall not be less than the value as stated in the instructions.

6.102 Temperature adjustment
6.102.1 Range adjustment

The allowed temperature setting range shall be limited by stops. Where applicable, the instructions shall

state the limits in which the temperature setting range may be adjusted using appropriate tools. The

temperature setting range stops shall not change on their own accord.
6.102.2 Set-point adjustment

If the adjusting knob is supplied as part of the thermostat, the marking of its positions shall be easily

recognizable. It shall indicate the direction in which the temperature is raised or lowered. If numbers are

used, higher numbers shall indicate higher temperatures, except for thermostats for refrigerators where

higher numbers shall indicate lower temperatures.

It shall be possible to select any temperature set-point over the whole temperature range by setting the

adjusting knob or spindle between the stops within the maximum and minimum ambient temperatures

as stated in the instructions.
The temperature setting means shall not change on its own accord.
6.102.3 Fixed setting thermostat

If provided, the adjuster of a fixed setting thermostat shall be sealed (e.g. lacquer).

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SIST EN 257:2022
EN 257:2022 (E)
7 Performance
7.1 General
Shall be according to EN 13611:2019, 7.1.
7.1.101 Sequence of testing
Tests shall be conducted in the sequence shown in Table 1.
Table 1 — Sequence of testing
Test
sample
Clause Test
1 2

7.2 Leak-tightness/Test for leak-tightness (except EN 13611:2019 6.3.2 / 6.3.3) X X

7.107 Effect of storage and transport temperatures X
7.108 Thermal overload of the temperature sensor X
7.101 Calibration temperature set-point X X
7.106 Ambient temperature range of the body X
7.102 Backlash X X
7.4 Rated flow rate/Test for rated flow rate X
7.105 Operating characteristic of the thermostat X
7.103 Opening of snap-acting thermostat with a closed position X

7.104 Opening pressure and closing pressure for thermostats with a closed position X

7.109 Operating torque of the thermostat set-point adjuster X X
7.3 Torsion and bending/Torsion and bending tests X

7.2 Leak-tightness/Test for leak-tightness (except EN 13611:2019 6.3.2 / 6.3.3) X

7.110 / 7.110.2.1 Endurance/Mechanical cycling test X
7.110 / 7.110.2.2 Endurance/Thermal cycling test X
7.109 Operating torque of the thermostat set-point adjuster X
7.102 Backlash X

7.2 Leak-tightness/Test for leak-tightness (except EN 13611:2019 6.3.2 / 6.3.3) X X

7.101 Calibration temperature set-point X X
7.5.3, 7.5.4 Resistance to scratching / Resistance to humidity X

7.101 / 7.105 Calibration temperature set-point/Operating characteristic of the thermostat X

EN 13611:2019,
Housing/Test for leakage of housing after removal of non-metallic parts X
6.3.2 / 6.3.3

Thermostats which can be converted to other gases by exchange of parts shall be supplied with these parts.

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SIST EN 257:2022
EN 257:2022 (E)
7.2 Leak-tightness
7.2.1 Requirements
EN 13611:2019, 7.2.1 is replaced by the following:

Thermostats shall be leak-tight in accordance with the leakage rates given in Table 2.

Table 2 — Maximum leakage rates
Maximum leakage rate
Nominal size
cm /h of air
(inlet)
DN a
External leak-tightness
Internal leak-tightness
DN < 10 60 20
10 ≤ DN ≤ 15 60 40
15 < DN ≤ 25 80 40
25 < DN ≤ 50 120 60
This requirement applies only to thermostats with complete shut-off.
7.2.2 Tests
7.2.2.1 General
Shall be according to EN 13611:2019, 7.2.2.1.
7.2.2.2 External leak-tightness
Shall be according to EN 13611:2019, 7.2.2.2.
7.2.2.3 Internal leak-tightness
Shall be according to EN 13611:2019, 7.2.2.3 with the following addition:

This test applies only to thermostats with complete shut-off. The knob is set at the middle of its

temperature setting range and the temperature sensor
...

SLOVENSKI STANDARD
oSIST prEN 257:2020
01-maj-2020
Mehanski termostati za plinske aparate
Mechanical thermostats for gas-burning appliances
Mechanische Temperaturregler für Gasgeräte
Thermostats mécaniques pour appareils à gaz
Ta slovenski standard je istoveten z: prEN 257
ICS:
17.200.20 Instrumenti za merjenje Temperature-measuring
temperature instruments
27.060.20 Plinski gorilniki Gas fuel burners
oSIST prEN 257:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
oSIST prEN 257:2020
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oSIST prEN 257:2020
DRAFT
EUROPEAN STANDARD
prEN 257
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2020
ICS 27.060.20 Will supersede EN 257:2010
English Version
Mechanical thermostats for gas-burning appliances

Thermostats mécaniques pour appareils à gaz Mechanische Temperaturregler für Gasgeräte

This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee

CEN/TC 58.

If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations

which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC

Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.

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.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without

notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 257:2020 E

worldwide for CEN national Members.
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oSIST prEN 257:2020
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Contents Page

European foreword ....................................................................................................................................................... 5

1 Scope ............................................................................................................................................................. 6

2 Normative references ............................................................................................................................. 7

3 Terms and definitions ............................................................................................................................ 7

4 Classification .............................................................................................................................................. 9

4.1 Classes of control ...................................................................................................................................... 9

4.2 Groups of control...................................................................................................................................... 9

4.3 Classes of control functions .................................................................................................................. 9

4.4 Types of DC supplied controls ............................................................................................................. 9

5 Test conditions and uncertainty of measurements .................................................................. 10

6 Design and construction ..................................................................................................................... 10

6.1 General ...................................................................................................................................................... 10

6.2 Mechanical parts of the control ....................................................................................................... 10

6.2.1 Appearance ............................................................................................................................................. 10

6.2.2 Holes .......................................................................................................................................................... 10

6.2.3 Breather holes ........................................................................................................................................ 10

6.2.4 Screwed fastenings ............................................................................................................................... 10

6.2.5 Jointing ...................................................................................................................................................... 10

6.2.6 Moving parts ........................................................................................................................................... 10

6.2.7 Sealing caps ............................................................................................................................................. 10

6.2.8 Dismantling and reassembly ............................................................................................................ 10

6.2.9 Auxiliary canals and orifices ............................................................................................................. 10

6.2.10 Presetting device ................................................................................................................................... 10

6.3 Materials................................................................................................................................................... 10

6.4 Gas connections ..................................................................................................................................... 11

6.5 Electrical parts of the control ........................................................................................................... 11

6.6 Protection against internal faults for the purpose of functional safety ............................ 11

6.101 Flow characteristics ............................................................................................................................. 11

6.102 Temperature adjustment ................................................................................................................... 11

6.102.1 Range adjustment ................................................................................................................................. 11

6.102.2 Set point adjustment ............................................................................................................................ 11

6.102.3 Fixed setting thermostat .................................................................................................................... 11

7 Performance ........................................................................................................................................... 12

7.1 General ...................................................................................................................................................... 12

7.2 Leak-tightness ........................................................................................................................................ 13

7.2.1 Requirements ......................................................................................................................................... 13

7.2.2 Tests ........................................................................................................................................................... 13

7.3 Torsion and bending ............................................................................................................................ 13

7.4 Rated flow rate ....................................................................................................................................... 13

7.4.1 Requirement ........................................................................................................................................... 13

7.4.2 Test ............................................................................................................................................................. 14

7.4.3 Conversion of air flow rate ................................................................................................................ 14

7.5 Durability ................................................................................................................................................. 14

7.6 Performance tests for electronic controls ................................................................................... 14

7.7 Long-term performance for electronic controls ........................................................................ 14

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7.8 Data exchange ......................................................................................................................................... 14

7.101 Calibration temperature set-point .................................................................................................. 14

7.101.1 Requirement............................................................................................................................................ 14

7.101.2 Test ............................................................................................................................................................. 14

7.102 Backlash .................................................................................................................................................... 14

7.102.1 Requirement............................................................................................................................................ 14

7.102.2 Test ............................................................................................................................................................. 15

7.103 Opening of a snap-acting thermostat with a closed position ................................................. 15

7.103.1 Requirement............................................................................................................................................ 15

7.103.2 Test ............................................................................................................................................................. 15

7.104 Opening pressure and closing pressure for thermostats with a closed position ........... 15

7.104.1 Requirement............................................................................................................................................ 15

7.104.2 Test ............................................................................................................................................................. 15

7.105 Operating characteristic of the thermostat ................................................................................. 15

7.105.1 Requirement............................................................................................................................................ 15

7.105.2 Test ............................................................................................................................................................. 16

7.106 Ambient temperature range of the body ...................................................................................... 19

7.106.1 Requirement............................................................................................................................................ 19

7.106.2 Test ............................................................................................................................................................. 19

7.107 Effect of storage and transport temperatures............................................................................. 19

7.107.1 Requirement............................................................................................................................................ 19

7.107.2 Test ............................................................................................................................................................. 20

7.108 Thermal overload of the temperature sensor............................................................................. 20

7.108.1 Requirement............................................................................................................................................ 20

7.108.2 Test ............................................................................................................................................................. 20

7.109 Operating torque of the thermostat set-point adjuster ........................................................... 20

7.109.1 Requirement............................................................................................................................................ 20

7.109.2 Test ............................................................................................................................................................. 20

7.110 Endurance ................................................................................................................................................ 20

7.110.1 Requirement............................................................................................................................................ 20

7.110.2 Tests ........................................................................................................................................................... 21

8 Electrical requirements ...................................................................................................................... 22

9 Electromagnetic compatibility (EMC) ............................................................................................ 22

10 Marking, installation and operating instructions ...................................................................... 22

10.1 Marking ..................................................................................................................................................... 22

10.2 Installation and operating instructions ........................................................................................ 22

10.3 Warning notice ....................................................................................................................................... 23

Annex A (informative) Abbreviations and Symbols ...................................................................................... 24

Annex B (informative) Leak-tightness tests for gas controls — volumetric method ........................ 25

Annex C (informative) Leak-tightness tests for gas controls — pressure loss method .................... 26

Annex D (normative) Calculation of pressure loss into leakage rate ..................................................... 27

Annex E (normative) Electrical/electronic component fault modes ...................................................... 28

Annex F (normative) Additional requirements for safety accessories and pressure

accessories as defined in EU Directive 2014/68/EU ................................................................ 29

Annex G (normative) Materials for pressurized parts ................................................................................. 30

Annex H (normative) Additional materials for pressurized parts .......................................................... 31

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Annex I (normative) Requirements for controls used in DC supplied burners and

appliances burning gaseous or liquid fuels ................................................................................. 32

Annex J (normative) Method for the determination of the Safety Integrity Level (SIL) .................. 33

Annex K (normative) Method for the determination of a Performance Level (PL)........................... 34

Annex L (informative) Relationship between Safety Integrity Level (SIL) and

Performance Level (PL) ...................................................................................................................... 35

Annex M (normative) Reset functions ............................................................................................................... 36

Annex N (informative) Guidance document on environmental aspects ............................................... 37

Annex O (normative) Seals of elastomers, cork and synthetic fibre mixtures .................................... 38

Annex AA (informative) Types of flame supervision devices.................................................................... 39

Annex ZA (informative) Relationship between this European Standard and the essential

requirements of Regulation (EU) 2016/426 aimed to be covered ..................................... 40

Bibliography ................................................................................................................................................................. 44

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European foreword

This document (prEN 257:2020) has been prepared by Technical Committee CEN/TC 58 “Safety and

control devices for burners and appliances burning gaseous or liquid fuels”, the secretariat of which is

held by BSI.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 257:2010.

This document has been prepared under a standardization request given to CEN by the European

Commission and the European Free Trade Association, and supports essential requirements of

EU Directive(s).

For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this

document.

prEN 257:2020 includes the following significant technical changes with respect to EN 257:2010:

a) scope is enlarged to maximum inlet pressures up to and including 50 kPa (500 mbar);

b) alignment with EN 13611:2019;
c) updating of Clause 2, normative references;

d) units of measurement and test conditions are updated according to EN 13611:2019;

e) requirements and tests concerning durability of elastomers in contact with gas (7.8 of this

document) are now totally aligned with EN 13611:2019, 7.8;

f) marking, installation and operating instructions (Clause 9 of this document) are extended to cover

additional information.
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Introduction

This document is intended to be used in conjunction with EN 13611:2019. This document refers to

clauses of EN 13611:2019 or adapts clauses by stating “with the following modification”, “with the

following addition”, “is replaced by the following” or “is not applicable” in the corresponding clause.

This document adds clauses or sub clauses to the structure of EN 13611:2019 which are particular to

this document. It should be noted that these clauses and subclauses are not indicated as an addition.

Subclauses which are additional to those in EN 13611:2019 are numbered starting from 101. Additional

Annexes are designated as Annex AA, BB, CC, etc.
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1 Scope

This document specifies the safety, construction and performance requirements for mechanical

thermostats intended for use with gas appliances and similar use, hereafter referred to as ‘thermostats’.

This document applies to thermostats with declared maximum inlet pressures up to and including

50 kPa (500 mbar) of nominal connection sizes up to and including DN 50 for use with one or more fuel

gases in accordance with EN 437.

This document applies to thermostats controlling the gas flow directly or indirectly through an integral

gas valve.

This document only applies to thermostats used with gas appliances which are not installed in the open

air.
Thermostats dealt with in this document are intended for control functions.
This document is not applicable to:
a) the thermocouple;

b) controls which use auxiliary energy (e.g. electrical energy supplied externally);

c) an assessment of the control regarding Performance Level (PL) and Safety Integrity Level (SIL).

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.

EN 13611:2019, Safety and control devices for burners and appliances burning gaseous and/or liquid

fuels — General requirements
3 Terms and definitions

For the purposes of this document, the terms and definitions given in EN 13611:2019 and the following

apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.101
mechanical thermostat

thermostat which controls the temperature by adjusting the flow rate accordingly to the temperature of

the sensor without any external energy, such that the temperature remains within defined limits

3.102
adjustable thermostat

mechanical thermostat in which the temperature set-point can be adjusted by the user to anywhere

between minimum and maximum values
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3.103
fixed setting thermostat

mechanical thermostat that has a preset fixed operating temperature which cannot be adjusted by the

user
3.104
snap-acting thermostat

mechanical thermostat with only two positions for the flow rate, i.e. ‘full on-off’, ‘full on-reduced rate’ or

‘reduced rate-off’
3.105
modulating thermostat

mechanical thermostat which controls the flow rate in accordance with a predetermined and

continuous function of the temperature of the temperature sensor
3.106
modulating thermostat with additional on-off action

mechanical thermostat which acts as a snap-acting thermostat between the closed and reduced

positions and as a modulating thermostat between the reduced and full-on positions

3.107
thermostat closure member

movable part of the thermostat which opens and closes the gas way and/or varies the flow rate

3.108
presetting device
device for adjusting an operating condition only by an authorized person

Note to entry: It may be fixed or variable, e.g. when it is the gas flow that is adjustable; either an orifice or an

adjusting screw may be used.
3.109
fixed bypass

non-adjustable presetting device for fixing the minimum gas flow through a thermostat

3.110
bypass adjusting device

screw adjustment or an exchangeable orifice, that fixes the minimum gas flow rate through the

thermostat, and which is accessible only by the use of tools
3.111
temperature sensor

device which senses the temperature of the medium to be controlled or to be supervised

3.112
operating curve

graphical representation of the flow rate as a function of the sensor temperature at a given temperature

set-point and at a constant inlet pressure
3.113
backlash

difference of position of the adjusting knob when it is moved in both directions to obtain the same flow

rate at a constant sensor temperature
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3.114
adjusting knob
adjustable spindle
part of the thermostat which is used to select the temperature set-point
3.115
temperature set-point

any value selected within the temperature range at which the controlled temperature should be

maintained
3.116
temperature set-point range
range between the minimum and maximum adjustable temperature set-points

Note 1 to entry: The temperature can be adjusted between the set-points by means of the adjusting knob.

3.117
calibration flow rate
flow rate declared by the manufacturer for calibration
3.118
calibration temperature set-point

temperature at which the calibration flow rate should be obtained with the adjustment set to the

position and in the direction declared by the manufacturer
3.119
temperature differential for snap-acting thermostats

difference in temperature necessary to obtain a change in the flow rate, at a given set-point

3.120
deviation

maximum deviation from the temperature set-point which is declared by the manufacturer

3.121
drift
permanent change in the operating curve of the thermostat
4 Classification
4.1 Classes of control
EN 13611:2019, 4.1 is not applicable.
4.2 Groups of control
Shall be according to EN 13611:2019, 4.2.
4.3 Classes of control functions
EN 13611:2019, 4.3 is not applicable.
4.4 Types of DC supplied controls
EN 13611:2019, 4.4 is not applicable.
NOTE See Scope.
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5 Test conditions and uncertainty of measurements
Shall be according to EN 13611:2019, Clause 5.
6 Design and construction
6.1 General
Shall be according to EN 13611:2019, 6.1.
6.2 Mechanical parts of the control
6.2.1 Appearance
Shall be according to EN 13611:2019, 6.2.1.
6.2.2 Holes
Shall be according to EN 13611:2019, 6.2.2.
6.2.3 Breather holes
Shall be according to EN 13611:2019, 6.2.3.
6.2.4 Screwed fastenings
Shall be according to EN 13611:2019, 6.2.4.
6.2.5 Jointing
Shall be according to EN 13611:2019, 6.2.5.
6.2.6 Moving parts
Shall be according to EN 13611:2019, 6.2.6.
6.2.7 Sealing caps
Shall be according to EN 13611:2019, 6.2.7.
6.2.8 Dismantling and reassembly
Shall be according to EN 13611:2019, 6.2.8 with the following addition:

If, in accordance with the manufacturers instructions the thermostat can be dismantled for servicing,

such action shall not result in a change in temperature calibration exceeding the declared maximum set

point deviation (see 7.101.1).
6.2.9 Auxiliary canals and orifices
Shall be according to EN 13611:2019, 6.2.9.
6.2.10 Presetting device
Shall be according to EN 13611:2019, 6.2.10.
6.3 Materials
Shall be according to EN 13611:2019, 6.3.
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6.4 Gas connections
Shall be according to EN 13611:2019, 6.4.
6.5 Electrical parts of the control
EN 13611:2019, 6.5 is not applicable.
NOTE See Scope.
6.6 Protection against internal faults for the purpose of functional safety
EN 13611:2019, 6.6 is not applicable.
NOTE See Scope.
6.101 Flow characteristics

An adjustable bypass shall be set by means of a variable presetting device or shall be adjusted by means

of a fixed presetting device.

It shall be possible to gain access to any fixed bypass or bypass adjusting device for cleaning without

changing the calibration temperature set-point.

The opening and closing of the thermostat closure member with a total shut-off function shall happen

by snap-action between the off position and the reduced flow position.

Figure 2 shows typical operating curves of a modulating, snap-acting and modulating on-off thermostat.

The flow rate at the moment of snap-action shall not be less than the value as stated in the operating

instructions.
6.102 Temperature adjustment
6.102.1 Range adjustment

The allowed temperature setting range shall be limited by stops. Where applicable the operating

instructions shall state the limits in which the temperature setting range may be adjusted using

appropriate tools. The temperature setting range stops shall not change on their own accord.

6.102.2 Set point adjustment

If the adjusting knob is supplied as part of the thermostat, the marking of its positions shall be easily

recognizable. It shall indicate the direction in which the temperature is raised or lowered. If numbers

are used, higher numbers shall indicate higher temperatures, except for thermostats for refrigerators

where higher numbers shall indicate lower temperatures.

It shall be possible to select any temperature set-point over the whole temperature range by setting the

adjusting knob or spindle between the stops within the maximum and minimum ambient temperatures

as stated in the operating instructions.
The temperature setting means shall not change on its own accord.
6.102.3 Fixed setting thermostat
If provided, the adjuster of a fixed set
...

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