A thermocouple (gas safety / flame failure device) is a safety component in gas cookers and ovens that shuts off the gas supply if the flame goes out. The tip of the thermocouple sits in the burner flame; when heated, it generates a small voltage that keeps the safety solenoid valve open. If the flame is lost, the thermocouple cools down, the voltage drops, and the valve closes to stop the gas flow.

Common fault symptoms include: the burner lights but goes out as soon as you release the knob; you have to hold the knob pressed for a long time; the flame goes out intermittently; or the thermocouple is not heating properly due to dirt or incorrect positioning. Typical fixes are cleaning the burner area and repositioning the thermocouple, checking connections, and replacing the thermocouple or the gas valve if needed.