Learning About Residential Furnaces

How To Diagnose And Replace A Thermocouple

Burning gas to create heat is potentially dangerous. To prevent disaster, furnace designers build several failsafes into a furnace. One of these failsafes is known as the thermocouple. Ordinarily, a thermocouple will not negatively affect the performance of your furnace, but when it begins to wear out, your furnace may not work at all. Thus, when you have a faulty thermocouple, you will need to make repairs quickly to get your furnace running like it should. 

What Is a Thermocouple?

Older furnaces will have a pilot light, which is a constantly burning flame. This flame ignites the gas when your furnace gets the signal from your thermostat to kick on. However, if the pilot light goes out, there will be no way to ignite the gas flowing into your furnace, and you will have a gas leak. A thermocouple has a bulb at one end that hangs over the pilot light. This bulb senses the heat from the pilot light and transforms it into electricity, which then opens a shut-off valve on the gas inlet line. As the thermocouple wears out, it will lose its ability to transform heat to electricity, and your furnace will stop working. 

Replacing a Thermocouple

Use these steps to replace a broken thermocouple:

1. Before you remove your old thermocouple, you will want to order a new one. 

2. Once the new part arrives, turn off the gas to you furnace at the shut-off valve in your furnace room. 

3. Turn off the electricity to your furnace at the breaker.

4. Locate the thermocouple and remove the bolts that hold it in place. 

5. Remove the old thermocouple and slide the new one into position. 

6. Replace the bolts that hold the thermocouple in place. 

7. Make sure that the bulb of the thermocouple hangs down over the pilot light without completely blocking the flame from the light. 

8. Turn the electricity and gas back on. 

As you can see, the steps to replacing a thermocouple are not super complicated, so you should be able to do the work on your own. You don't have to be versed in electrical engineering or furnace repair in order to replace a thermocouple. In fact, you only need to have a basic skill level with wrenches. On the other hand, a furnace is a key piece of equipment in your home, and even a small problem with the electrical or gas components of you furnace can cause problems. If you have any question about your ability to repair your thermocouple, you should call in a professional for furnace repairs


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