What does a typical thermocouple used on a gas furnace do?

In a gas furnace, a typical thermocouple plays a crucial role in safety and operation by generating a small DC voltage. This occurs due to the thermoelectric effect, where the junction of two dissimilar metals produces a voltage that is proportional to the temperature difference between the hot junction (where the flame is) and the cold junction (where the thermocouple connects to the control circuit).

This generated voltage is critical for ensuring that the gas valve remains open during operation. If the flame goes out, the thermocouple cools and ceases to generate the voltage, leading to the closure of the gas valve, which prevents gas leaks and potential hazards.

Understanding the function of the thermocouple is important in diagnosing furnace issues and ensuring safe operation. Its role in generating a small DC voltage directly ties into how the furnace operates and responds to temperature changes, confirming its primary purpose in this context.