Thermocouple Function

• A thermocouple is a probe that is part of your gas furnace's pilot light component. The probe is a self-contained unit that contains a copper wire that connects the component to the gas valve. It sits directly in front of the flame and acts as a sensor, sending a low-voltage signal to the gas valve, informing it that a flame is present and to keep supplying gas to the flame. If the flame ever goes out, due to wind or another safety component inside the furnace shutting off the flame, the thermocouple sends a signal to the gas valve to shut off the gas flow.
  
  

Failure Symptoms

• Thermocouples do not last forever. Warning signs of a bad thermocouple include a pilot light not igniting, the pilot light shutting off repeatedly and the pilot light going out shortly after lighting it with a match.
  
  

Replacement

• You can purchase a thermocouple for your furnace directly from the appliance's manufacturer or a furnace/equipment supply store as well as from an online furnace parts outlet. Replace the probe yourself according to the directions and recommendations in your furnace's repair manual. or contact a furnace repair service and have it order the probe for you.
  
  

Warnings

• If you are not handy with tools and furnace repair, do not attempt to replace the thermocouple or tamper with your furnace's pilot light yourself. Doing so is a fire/explosion risk; you could cause damage to your furnace, if not injure yourself. Have a professional repair service do the job.