What Is a Thermocouple?


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Your furnace could get a hefty workout during the winter months, depending on where you live. As the temperatures outside plummet, your furnace may have to work overtime to keep your home warm and comfortable. However, once you switch on your heat, your furnace and HVAC system have to go through a complex process before warm air blows through your vents. Your furnace is a complicated appliance, relying on combustible materials, high temperatures, and properly functioning equipment. As a result, homeowners often express concern about the safety of having a gas-powered furnace. For the most part, these concerns are unfounded.

Routine maintenance once a year is the best way to ensure that your furnace is safe and operating effectively. Your gas furnace should function properly and present very few health or safety hazards with care and service. One way manufacturers limit any potential risks is with a device called a thermocouple. This device is built into all gas furnaces to protect against gas leaks and fire or explosion risks. So, what is a thermocouple? Let’s take a look at the safety device in your furnace that works to protect your home and family.

What is a furnace thermocouple?


The thermocouple is a safety device used to detect the pilot light flame. It is installed so that the ends of the probe are in the pilot flame or very close to it. The thermocouple detects the heat from the pilot light flame and controls the valve allowing gas into the chamber. If the pilot light goes out or malfunctions, the thermocouple will automatically shut off the gas valve. This will prevent unburned gas from leaking into the combustion chamber, where a small spark could ignite an explosion.

The thermocouple performs through a thermoelectric effect known as the “Seebeck effect.” The idea is that two different metals close to each other will produce an electrical voltage in proportion to the heat they sense. The higher the heat, the higher the voltage. A thermocouple operates with this principle keeping the gas valve open with electric voltage. If the pilot light goes out, the two pieces of metal on the thermocouple stop producing electric voltage, and the gas valve is shut off. A properly functioning thermocouple significantly reduces the risk of a gas leak or fire.

What can go wrong with the thermocouple?


Just like any other part of your heating system, the thermocouple can wear out over time and can be susceptible to rust, dirt, dust, and debris. Throughout the normal operation, your thermocouple could also fall out of place and fail to detect a flame because it is too far away from the pilot light. The most common problem that many homeowners experience is a dirty thermocouple. If substances build up on the metal strips, this could cause improper readings, and your gas valve would be shut off. Additionally, the wires can become loose, or the thermocouple might need to be recalibrated occasionally.

It is important to note that thermocouples are not designed to last the entire lifetime of your unit. Your furnace could last around 20 years or more. However, you may have to replace the thermocouple a few times during that life span. The good news is that when a thermocouple goes bad or malfunctions, your home is still safe, as the gas flowing to the unit will be shut off. On the downside, when the device stops working, you will not have heat until it is fixed.

The thermocouple is an important safety device that you can find on any gas-fueled appliance. Inside of your gas furnace, the thermocouple keeps your home and family safe by preventing dangerous gas leaks. Regular annual maintenance and routine air filter changes will help keep your thermocouple functioning and allow your home to be comfortable all winter long.