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An Overview of the Furnace Thermocouple

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If you have an older furnace, then it probably has a thermocouple. You will find thermocouples in old furnaces that use pilot lights instead of the electric ignitions in relatively newer furnaces. A thermocouple is a critical part of the furnace, and you should understand it, just as you should other parts of the furnace. Below is an overview of this furnace part.

How It Works

The thermocouple comprises two different metals that generate electricity when heated. One end of the thermocouple sits above the pilot light while the other end connects to the gas valve.

When you light the pilot light, its flame heats the thermocouple and generates electricity. The electrical current flows to the gas valve sensor, which keeps the valve open and allows the gas to flow and keep the furnace burners on.

The electrical flow through the thermocouple ceases when you switch off the furnace. The gas valve closes in response and cuts off the gas supply to the burners.

Why It’s Necessary

The thermocouple services two critical functions.

Preventing Gas Buildup

The thermocouple ensures that fuel only flows to the combustion chamber if the pilot light burns. This restriction is critical because any fuel that flows to the combustion chamber should burn. Otherwise, fuel would build up in the chamber and explode the next time you light the pilot light. Such explosions are not only fire risks, but they can also damage the furnace.

Preventing Gas Leak

The furnace gas won’t necessarily stay within the combustion chamber if it doesn’t burn. Some of the gas might escape and circulate in the house. Inhaling natural gas is not good for your health or your pet’s health. The gas is also a fire risk; it can explode the next time you light a fire in the house. The thermocouple action prevents such gas leakage.

What Its Potential Problems Are

The thermocouple is subject to malfunctions, just as other furnace parts. Below are some problems the thermocouple might experience.

Debris Buildup

Various forms of debris can clog the thermocouple. The clogging can insulate the metal and reduce heat transfer from the pilot light. The thermocouple might delay the signal relay to the gas valve sensor. Alternatively, the thermocouple will behave as if the pilot light is off and close the gas supply. Corrosion, mold, and dust are some debris that can trigger such problems.

Wear and Tear

The thermocouple metal will suffer wear and tear over its life. Corrosion, as well as constant expansion and contraction, are some of the things that will determine the thermocouple’s wear and tear. A worn thermocouple is not effective.

Loose Connections

The thermocouple can also malfunction if it loses its electrical connection to the gas valve sensor. In such a case, the gas valve won’t sense when the pilot light is on, which means gas won’t flow to the burners.

What Signs of Thermocouple Malfunctions Are

Fortunately, you will know when your thermocouple malfunctions. Below are two signs of such malfunctions.

Sudden Loss of Heat

You should suspect a thermocouple malfunction if you have gas and the pilot light comes on but then goes off after a few seconds. That sign means the gas valve sensor does not get the signals it needs to stay open.

Gas Leak

You should also suspect a thermocouple issue if you have a gas leak in the house. That might be the case if your gas detector alarm goes on and you rule out alternative causes of the leak.

CABS Heating & Air Conditioning installs, services, and maintains various forms of HVAC systems. We have years of experience in the HVAC industry. Contact us for a quote on your HVAC needs and enjoy our professional services.

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