scope:

This part of ISO 23551 specifies safety, constructional and performance requirements and testing of mechanical gas thermostat for gas burners, gas appliances and similar use, hereafter referred to as 'thermostats'. This ISO Standard covers type testing only. This ISO standard applies to mechanical gas thermostats of nominal connection sizes up to and including DN 50 with declared maximum inlet pressures up to and including 50 kPa for burners and gas-burning appliances using fuel gases as natural gas, manufactured gas, and liquefied petroleum gas (LPG). This ISO standard applies to mechanical 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 ISO standard only applies to mechanical thermostats used on gas appliances where the thermostat is not directly exposed to the outdoor environment. This ISO standard only applies to mechanical thermostats which are intended for operating control functions.