ISO 23551-6:2021

Safety and control devices for gas burners and gas-burning appliances - Particular requirements - Part 6: Thermoelectric flame supervision controls

This document specifies safety, constructional, and performance and testing requirements for thermoelectric flame supervision controls, energized by a thermocouple, intended for use with gas burners and gas-burning appliances, hereafter referred to as “controls”. This document applies to thermoelectric flame supervision controls for gas burners and gas-burning appliances of nominal connection size up to, and including DN 50, that can be used and tested independently of these appliances. These thermoelectric flame supervision controls are suitable for fuel gases, such as natural gas, manufactured gas or liquefied petroleum gas (LPG) at inlet pressures up to and including 50 kPa. It is not applicable to corrosive and waste gases. This document covers type testing only. This document is not applicable to: a) the thermocouple; and b) controls which use auxiliary energy (e.g. electrical energy supplied externally).

Dispositifs de commande et de sécurité pour brûleurs à gaz et appareils à gaz — Exigences particulières — Partie 6: Équipements thermoélectriques de surveillance de flamme

General Information

• Status: Published
• Publication Date: 31-Oct-2021
• ICS: 27.060.20 - Gas fuel burners
• Technical Committee: ISO/TC 161 - Controls and protective devices for gas and/or oil
• Drafting Committee: ISO/TC 161/WG 4 - Multifunctional Controls
• Current Stage: 6060 - International Standard published
• Start Date: 01-Nov-2021
• Due Date: 15-Aug-2022
• Completion Date: 01-Nov-2021

Relations

• Revises: ISO 23551-6:2014 - Safety and control devices for gas burners and gas-burning appliances - Particular requirements - Part 6: Thermoelectric flame supervision controls
• Effective Date: 23-Apr-2020

Overview

ISO 23551-6:2021 specifies safety, constructional, performance and type-testing requirements for thermoelectric flame supervision controls energized by a thermocouple for use with gas burners and gas-burning appliances. The standard applies to controls for nominal connection sizes up to and including DN 50, suitable for fuel gases such as natural gas and LPG at inlet pressures up to and including 50 kPa. It covers type testing only and expressly excludes the thermocouple itself, controls using auxiliary energy (e.g., externally supplied electrical energy), and use with corrosive or waste gases. ISO 23551-6:2021 is intended to be used in combination with ISO 23550 to form the complete set of product requirements.

Key Topics

The standard focuses on practical, testable requirements for reliable and safe operation of thermoelectric flame supervision controls. Major technical topics include:

• Construction requirements: materials, moving parts, sealing caps, breather/vent limits, and serviceability.
• Connections and fittings: connection types, threads, union joints, flanges, compression fittings and gas quick connectors (GQC).
• Performance and functional tests: leak-tightness (volumetric and pressure-loss methods), rated flow, torsion and bending, operating torque/force, sealing force and closing current.
• Durability and endurance: mechanical endurance tests, vibration testing and functional endurance under specified conditions.
• Electrical and EMC considerations: requirements where electrical equipment is present and electromagnetic compatibility testing.
• Marking and documentation: marking, installation and operating instructions, and warning notices required for safe use.
• Annexes and regional requirements: test methods (leakage conversion), material resistance (elastomers), GQC details, and specific regional rules (Annexes F, G, H).

Applications

ISO 23551-6:2021 is directly applicable to organizations and professionals involved with gas safety and control devices:

• Manufacturers designing and certifying thermoelectric flame supervision controls.
• Test laboratories and certification bodies performing type testing for compliance.
• Design and safety engineers specifying components for gas burners, boilers, and industrial appliances.
• Procurement and quality teams drafting specifications and acceptance criteria.
• Regulators and installers seeking harmonized safety and marking requirements.

Using ISO 23551-6 helps reduce risk of flame failure, ensures reliable thermocouple-energized control behavior, and supports regulatory compliance and market access for gas appliance components.

Related Standards

• ISO 23550 (general requirements for safety and control devices for gas burners and appliances) - used in combination with ISO 23551-6 for full product requirements.
• Refer to regional normative annexes within ISO 23551-6 for country-specific provisions (Europe, North America, Japan).

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 23551-6
Second edition
2021-11
Safety and control devices for gas
burners and gas-burning appliances —
Particular requirements —
Part 6:
Thermoelectric flame supervision
controls
Dispositifs de commande et de sécurité pour brûleurs à gaz et
appareils à gaz — Exigences particulières —
Partie 6: Équipements thermoélectriques de surveillance de flamme
Reference number
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Classification . 2
4.1 Classes of controls . 2
4.2 Groups of controls . 2
4.3 Types of DC supplied controls . 2
4.4 Classes of control functions . 2
5 Test conditions and tolerances .3
6 Construction . 3
6.1 General . 3
6.2 Construction requirements. 3
6.2.1 Appearance . 3
6.2.2 Holes . 3
6.2.3 Breather holes . 3
6.2.4 Vent limiter . 3
6.2.5 Screwed fastenings . 3
6.2.6 Moving parts . 3
6.2.7 Sealing caps . 3
6.2.8 Disassembling and assembling for servicing and/or adjustment for controls . 3
6.2.9 Auxiliary channels and orifices . 3
6.2.10 Pre-setting device . 3
6.3 Materials . 4
6.4 Connections . 4
6.4.1 General . 4
6.4.2 Connection sizes . 4
6.4.3 Connection types . 4
6.4.4 Threads . 4
6.4.5 Union joints . 4
6.4.6 Flanges . 4
6.4.7 Compression fittings . 4
6.4.8 Flare connections . 4
6.4.9 Nipples for pressure tests . 4
6.4.10 Strainers . . . 4
6.4.11 Gas connections by GQC . 4
6.5 Gas controls employing electrical components in the gas way . 4
7 Performance . 5
7.1 General . 5
7.2 Leak-tightness . 5
7.2.1 General . 5
7.2.2 Requirements . 5
7.2.3 Test . . . 5
7.3 Torsion and bending . 6
7.4 Rated flow rate . 6
7.5 Durability . 6
7.6 Functional requirements . . 6
7.6.1 Operating torque and force . 6
7.6.2 Interlocks . 7
7.6.3 Sealing force . 8
7.6.4 Closing current . 8
iii
7.7 Endurance . 8
7.7.1 Requirements . 8
7.7.2 Endurance test . 8
7.8 Vibration test . 9
8 Electrical equipment . 9
9 Electromagnetic compatibility (EMC) .10
10 Marking, installation and operation instructions .10
10.1 Marking . 10
10.2 Installation and operating instructions . 10
10.3 Warning notice . 10
Annex A (informative) Leak-tightness test — Volumetric method .11
Annex B (informative) Leak-tightness test — Pressure-loss method .12
Annex C (normative) Conversion of pressure loss into leakage rate .13
Annex D (normative) Gas quick connector (GQC) .14
Annex E (normative) Elastomers/requirements resistance to lubricants and gas .15
Annex F (normative) Specific regional requirements in European countries .16
Annex G (normative) Specific regional requirements in Canada and USA .17
Annex H (normative) Specific regional requirements in Japan .18
Annex I (informative) Types of flame supervision controls .19
iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 161, Control and protective devices for gas
and/or oil burners and appliances.
This second edition cancels and replaces the first edition (ISO 23551-6:2014), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— updated to align technically and with the revised format of the latest edition of ISO 23550;
— relocation of specific regional requirements into the main body of the standard that were previously
contained in regional annexes.
A list of all parts in the ISO 23551 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
Introduction
This document is designed to be used in combination with ISO 23550. Together with ISO 23550, this
document establishes the full requirements as they apply to the product covered by this document.
Where needed, this document adapts ISO 23550 by stating in the corresponding clause:
— “with the following modification”;
— “with the following addition”;
— “is replaced by the following”; or
— “is not applicable”.
In order to identify specific requirements that are particular to this document, and that are not already
covered by ISO 23550, this document can contain clauses or subclauses that are additional to the
structure of ISO 23550. These subclauses are indicated by the introductory sentence: “Subclause (or
Annex) specific to this document.”
To ensure global relevance of this document, the differing requirements resulting from practical
experience and installation practices in various regions of the world have been taken into account. The
variations in basic infrastructure associated with gas and/or oil controls and appliances have also been
recognized, some of which are addressed in Annexes F, G and H. This document intends to provide a
basic framework of requirements that recognize these differences.
vi
INTERNATIONAL STANDARD ISO 23551-6:2021(E)
Safety and control devices for gas burners and gas-burning
appliances — Particular requirements —
Part 6:
Thermoelectric flame supervision controls
1 Scope
This document specifies safety, constructional, and performance and testing requirements for
thermoelectric flame supervision controls, energized by a thermocouple, intended for use with gas
burners and gas-burning appliances, hereafter referred to as “controls”.
This document applies to thermoelectric flame supervision controls for gas burners and gas-burning
appliances of nominal connection size up to, and including DN 50, that can be used and tested
independently of these appliances.
These thermoelectric flame supervision controls are suitable for fuel gases, such as natural gas,
manufactured gas or liquefied petroleum gas (LPG) at inlet pressures up to and including 50 kPa. It is
not applicable to corrosive and waste gases.
This document covers type testing only.
This document is not applicable to:
a) the thermocouple; and
b) controls which use auxiliary energy (e.g. electrical energy supplied externally).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 2355
...