A thermocouple is a temperature-sensing device that generates a small electrical current when heated, serving as a safety control to shut off gas supply if the pilot light extinguishes. Composed of two different metal wires joined at a junction, thermocouples produce 15 to 30 millivolts when exposed to pilot light heat. This voltage holds open a solenoid safety valve, allowing gas flow to the burner.
Technical Function and Safety
When pilot light temperature drops due to flame extinguishment, thermocouple voltage decreases, causing the safety valve to close within 30 to 60 seconds. This prevents unburned gas from accumulating in the furnace or appliance. Thermocouples are positioned 0.5 to 1 inch from the pilot flame tip for optimal response. Annual inspections ensure proper thermocouple positioning and electrical continuity.
Maintenance and Replacement
Thermocouple lifespan typically ranges from 10 to 15 years before electrical drift occurs, requiring replacement at costs of 40 to 100 dollars. Common failure signs include frequent pilot light outages or reluctance to stay lit. Cleaning the thermocouple tip removes oxidation and can restore function temporarily. Thermocouples remain standard safety devices in standing pilot systems, while modern furnaces with electronic ignition use flame sensors and solid-state controls instead.