In a properly functioning gas furnace, the thermocouple is responsible for:

In a properly functioning gas furnace, the thermocouple plays a critical role in detecting the presence of a flame. It is a safety device that senses the heat generated by the flame in the burner. If the flame is present, the thermocouple produces a small electrical voltage that keeps the gas valve open, allowing gas to flow to the burner. If the flame goes out, the thermocouple cools down, resulting in a loss of voltage that signals the gas valve to close, thus preventing any unburned gas from being released, which could be hazardous.

This function is essential for the safe operation of the gas furnace. By ensuring that gas is only released when there is an active flame, the thermocouple helps prevent dangerous situations such as gas leaks or potential explosions.

Other options like measuring airflow or regulating water temperature do not fall under the thermocouple's responsibilities, as these tasks are typically managed by different components within the furnace system.