ISO 23551-6:2021

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).