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Clear Spring Heating Repair Question: What Does a Furnace Thermocouple Do?

Modern appliances are equipped with an array of safety measures to make sure that they operate safely in your Clear Spring home. This includes gas furnaces, which are harmless when working correctly but can be unsafe if something goes wrong. Perhaps the most crucial safety feature of a gas furnace is the thermocouple, also called a flame sensor.

Essentially, a furnace thermocouple works as a kill switch to shut off the furnace in case the gas is not igniting, like if the pilot light is out. Here is how it works.

The thermocouple is made up of two pieces of metal which are welded together at one end, called the “hot end” because it actually sits directly in the path of the furnace flame. On the cold end, it is wired to a circuit. Under normal circumstances, when the furnace is switched on, gas flows through the line and is ignited by a pilot light, ignition spark or glow coil. The flame heats up the thermocouple, and the furnace stays on.

However, sometimes the gas may not ignite, for example if the pilot light is out or the glow coil is faulty. In these cases, if there were no thermocouple, gas would continue to flow out without being lit, creating a very dangerous, poisonous and potentially lethal situation.

What the thermocouple does is detect heat, so if the furnace is on, but the hot end of the thermocouple has not heated up, that circuit up at the cold end kills the power to the furnace so that gas cannot continue to flow out unchecked. That way, you do not have to worry about a gas leak building to dangerous levels without being aware of it.

Sometimes, the thermocouple can malfunction, causing the furnace to shut off even if the burners are working just fine. Usually that is just the result of build up on the hot end over time, which can be fixed with some sand paper or emery cloth. If suspect a problem with your furnace, give Larry & Sons Plumbing, Heating & Air Conditioning a call!