HeatingWhat Is a Thermocouple?

Have you ever wondered about how your pilot light actually works? Ever had it refuse to stay lit for some strange reason? One of the most vital parts of your furnace or boiler is the pilot light, but one of the most vital parts of that is the thermocouple. It is this small part that allows the pilot light to do its job, while simultaneously keeping you safe. Let’s examine the thermocouple more closely.


A thermocouple is actually a rod or wire made of two different metal conductors. One end of this wire is close to the pilot light, so it can absorb its heat. The other end is hooked up to the gas valve that controls the flow of gas to the pilot light, keeping it lit.

Because of a principle called the “Seebeck Effect,” any conductor will produce an electric charge when submitted to varying levels of heat. The thermocouple is made of two different conductors to both increase the heat gradient and allow more precise tuning. Essentially, this wire acts as a sort of electric thermometer.


When the thermocouple senses heat from the pilot light, it generates an electric charge that is relayed to the gas valve. The gas valve opens, providing a steady stream of fuel to keep the pilot light going after it has been lit. This is how the pilot light stays burning 24/7. As long as the thermocouple is absorbing heat from the pilot light, the pilot light will keep going.

So what happens when the pilot light blows out? When the thermocouple no longer senses the heat from the pilot light, it loses its electrical charge and the gas valve shuts. This is a safety feature to prevent the home from filling with gas when the pilot light is out.

A bad thermocouple will have trouble keeping a pilot light lit, because for whatever reason it is unable to sense the heat from the flame and produce a charge. If your pilot light won’t stay lit, you likely need to replace the thermocouple.

If you are having problems with your pilot light, call G&S Heating, Cooling & Electrical, Inc. Our heating professionals cover all of Everett.


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