NBN EN 257:2010

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.