This part is fitted to the older standard efficiency Chaffoteaux boilers that have a permanent pilot light, they are an early way of detecting if there is a flame present. They are made from 2 dissimilar metals that when heated generates a small electrical current that is then sent down to the gas valve to hold in the pilot solenoid on the gas valve allowing the user to let go of the knob. If the pilot light goes out for any reason the thermocouple cools down, the electrical current decreases allowing the pilot solenoid to drop out. Once the pilot solenoid has dropped out the gas to the burner is extinguished and the Chaffoteaux boiler is switched off for safety.
Chaffoteaux 60074432 Celt Star Thermocouple

Part: 60074432

Price: £32.09
Chaffoteaux 60057703 Flexiflue Thermocouple

Part: 60057703

Price: £15.20