kSIST FprEN 257:2022

Mechanical thermostats for gas-burning appliances

This European Standard 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 European Standard 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 European Standard applies to thermostats controlling the gas flow directly or indirectly through an integral gas valve, and which do not require external electrical energy for their operation.
This European Standard only applies to thermostats used with gas appliances which are not installed in the open air.
Thermostats dealt with in this European Standard are intended for control functions.

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: Not Published
• Public Enquiry End Date: 02-Jun-2020
• ICS: 17.200.20 - Temperature-measuring instruments
• ICS: 27.060.20 - Gas fuel burners
• Technical Committee: PLN - Gas appliances for domestic use
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 26-Oct-2022
• Due Date: 31-Dec-2022
• Directive: 2014/68/EU - Directive 2014/68/EU of the European Parliament and of the Council of 15 May 2014 on the harmonisation of the laws of the Member States relating to the making available on the market of pressure equipment
• Directive: 2016/426 - REGULATION (EU) 2016/426 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 9 March 2016 on appliances burning gaseous fuels and repealing Directive 2009/142/EC
• Mandate: M/BC/CEN/89/6 - Standardization request to CEN concerning appliances burning gaseous fuels
• Ref Project: EN 257:2022 - Mechanical thermostats for gas-burning appliances

RELATIONS

• Revised: SIST EN 257:2010 - Mechanical thermostats for gas-burning appliances
• Effective Date: 01-May-2020
• Replaces: SIST EN 257:2010 - Mechanical thermostats for gas-burning appliances
• Effective Date: 19-Oct-2022

Standards Content (sample)

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.

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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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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
...