The Williams Comfort Products P043801 Thermocouple is a temperature-sensing safety component designed for gas-fired HVAC equipment, including Williams wall furnaces and heaters. It operates by sensing the pilot flame and generating a small electrical signal that allows the gas valve to remain open when the flame is present. If the pilot flame goes out, the thermocouple stops producing... https://www.partshnc.com/p043801-williams-comfort-products-thermocouple