Thermocouples are made by joining two different metals and connecting each one to a separate wire. This allows them to generate a small electrical signal, up to 30 millivolts, used by the ignition control system to verify the pilot light or burner is lit.

Thermopiles are made of multiple thermocouples connected in series to create voltages up to 750 millivolts when exposed to high heat or flame. This voltage can operate small valves and other components in places where external power is not wired. They are commonly used as positive feedback sensors to maintain the flame in a burner or pilot light.