Resideo Q340A1090 36" Thermocouple 30mV

The Resideo Q340A1090 is a 36-inch thermocouple, a critical safety component in gas-fired HVAC systems with pilot lights. It works by converting heat into a small electrical voltage, typically between 26 and 32 millivolts (not 30 volts as listed). The pilot flame heats the tip of the thermocouple, creating a temperature difference from the base. This difference generates a current that signals the gas control valve to stay open, allowing gas flow to the burner. If the pilot goes out, the thermocouple cools down, the voltage drops, and the gas control valve shuts off the gas supply as a safety measure. This 36-inch length provides greater flexibility during installation in various furnaces and boilers.