How To Replace A Broken Or Defective Gas Furnace Thermocouple

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How To Replace A Broken Or Defective Gas Furnace Thermocouple

How To Replace A Broken Or Defective Gas Furnace Thermocouple

14 December 2016
 Categories:
, Blog


If your natural gas furnace has stopped working, one of the first places you should check is the thermocouple. This simple but vitally important device maintains the safety of your furnace and prevents a potentially devastating fire or explosion. However, if it fails to work as it should, you will not be able to turn on your furnace. Fortunately, replacing this component is relatively easy and is also a low-cost repair. Below is more information about the humble thermocouple and how to perform a replacement:

What a thermocouple does

For gas furnaces that use a pilot light, the thermocouple serves as a monitoring device for the presence of a flame. One end of the thermocouple is extended into the flame space on the pilot light, while the opposite end is attached to the furnace's control system. If the thermocouple detects the pilot light flame, then the system has an "all clear" to light the main burners whenever a call for heat is sent to the unit. Likewise, if the thermocouple does not detect a pilot light, it will automatically shut down the gas supply to both the pilot light and the main burners, thus preventing the release of large volumes of unburned natural gas. As with any electro-mechanical device, a worn or broken thermocouple will provide a false indication of a problem with the pilot light and prevent it from sustaining itself or ignite the burners.

How to replace the thermocouple

Fortunately, the thermocouple replacement job is not difficult and should only take a few minutes. Here are a few steps you can take to smoothly change out a defective thermocouple with a new one:

1. Turn off the system completely — Begin by disconnecting both the natural gas supply and electrical supply to the system; there will be a main gas valve located in close proximity to the unit, and turning this off entails turning it clockwise. Most gas valves will be gate valves, which only need to be moved about 90 degrees to the right to shut off the gas. For the electrical supply, there should be a switch located near the system, and this simply needs to be flicked off like a wall switch. If you can't locate a switch, then turn off the relevant breaker at the circuit breaker panel.

2. Remove the old thermocouple — After disconnecting the power and gas supply, locate the thermocouple and make a careful note of how it it is attached. In most cases a few turns of a screwdriver or wrench will easily remove the flame sensing end near the pilot light. Disconnect the thermocouple and set the flame sensing probe aside. Next, locate the other end of the thermocouple where it attaches to the unit and remove it by unscrewing or unbolting it.

3. Select and install a new thermocouple — Once the old thermocouple is out of the way, buy a unit that is compatible with your furnace. You may need to check with a parts supplier or reputable HVAC dealer or service provider for additional help. Installation of the new unit is easy, as you simply need to reattach the end to the countrol panel while reattaching the other end to the space adjacent to the pilot light. Restore power and gas to the unit, and test it for successful operation.

For more information, contact local professionals like HELP Plumbing, Heating, Cooling and Electric.

About Me
heating and cooling a tranformed attic

When my husband and I made the decision to transform the attic into a home office, we didn't think about how that would impact our home heating and cooling system. This space has been complete for about a year now, and it is always cold in the winter and hot in the summer. We decided that, before this winter hit, we would have an HVAC technician come out and see what could be done to improve the heating and cooling of the space. Find out what you can do to heat and cool these areas of the home here on my blog.