The thermocouple is a heat-sensitive device placed on a gas fireplace. When the pilot is turned on, it sends a small electrical signal to the gas valve and keeps the gas valve open. This is an essential part of your fireplace, which does not burn the pilot if it fails, and when the pilot fails, the fireplace also stops working.

Gas fireplace soldiers primarily use thermocouples and thermopile devices to generate electricity. Thermocouples act as a sensor for gas flow. It supplies gas to the pilot light through a gas valve.

What Is a Thermocouple?

A thermocouple is a device made of two different metals that are joined together at one end. When this junction is heated, a small voltage is created that can be used to measure temperature.

A thermocouple is used to sense the temperature of your gas fireplace. It is placed in the pilot light assembly and if the pilot light goes out, the gas flow to the fireplace is shut off.

How to Work Thermocouple?

The thermocouple has a long copper tube. It has a probe at one end and threaded fittings at the other end that rotate towards the gas valve.

The thermocouple is a connection between two different types of metals, this connection creates a voltage relative to the temperature. This voltage is mainly used to control the main gas. This voltage produced is measured in millivolts. Its main power is the pilot light.

With this system you will have a pilot light in your fireplace, it will remain uninterrupted even if your fireplace is off. Wall switches and remote controls are can be used to turn the burner flame on and off.

You will not have a pilot light in the IPI system, which will run when the fireplace is off like millivolts. In this system, you will ignite the pilot with an automatic spark igniter before igniting the burner. You can use a wall switch, remote control, or toggle switch to turn on the fireplace.

Whenever you turn on the switch, you will hear clicking sounds from the igniter sparking. Remember, if the thermocouple fails, your fireplace will shut down.

How to Test Thermocouple on Gas Fireplace?

The thermocouple is a protection device that controls the gas supply to the gas-heated fireplace. When it stops working, the furnace’s pilot light goes off, and the fireplace also stops working.

If you don’t get pilot lighting, check the thermocouple and repair your fireplace to keep your home safe and warm all year round. 

Check the Pilot Light

If your thermocouple doesn’t work, the pilot light doesn’t turn on, you can’t always be sure that the thermocouple is the problem. It may be that the pilot gas tube is closed. If this is the case, the flame will not be strong enough to heat the temperature to the right temperature.

First, illuminate the pilot and observe the size and quality of the flame. It should be mostly blue. Will burn slowly and will be large enough to attach the thermocouple probe. The pilot tube is closed if it is not yellow or orange, irregularly shaped, and unstable. Clean it.

Visually Inspect

You can also test the thermocouple to test visually. Check the thermocouple tube for your water symptoms in it, it will affect the activity of the thermocouple. Make sure using a wrench, the nut is tightly attached to the valve. The work has to be done with very skilled hands.

Test With a Multimeter

This is the most reliable way to test. To identify bad thermocouples in this test, use a multimeter with a lead alligator clip. Set the meter to read dc millivolts. Now carefully clip one lead to the thermocouple probe, and the other to the tube near the gas valve.

Then turn on the pilot, let it burn for 30 seconds, and write down the reading. If something less than 25 mv is observed, you can think of it as a faulty thermocouple.

How to Clean a Thermocouple on a Gas Fireplace?

Your thermocouples in a gas fireplace can be clogged with dirt or soot. This is very harmful to thermocouples, which will reduce the effectiveness of thermocouples. Cleaning thermocouples is not a very complicated process, but it can’t be done at any time, especially when the fireplace is hot. To clean it, first, you need to turn off the fireplace and cool it completely.

Your thermocouple has been sitting directly on the flame all his life. Therefore, it is not impossible to get a carbon deposit buildup after one season of the use of a thermocouple.

If at the end of a sudden inspection you determine that it has a carbon buildup, don’t look for alternatives to clean it. Try to do this through a strip of fine-grit sandpaper. Rub it lightly until it ignites again. Often, you will find enough to fix a fireplace that will not be lit.

In other ways, first, close the fire valve gas valve and remove the front panel from the fireplace. Some panels have a screw on each side to remove them. Now find the thermocouple (it is located next to the pilot light and should look like a small straight pipe).

Then gently remove any dust and dirt (if any) from the thermocouple. You can use a can of compressed air for this. Now close the fireplace access panel, turn on the gas supply to the fireplace again, and re-light.

If that doesn’t work, call a technician. Thermocouple repair or replacement is not expensive, or difficult enough.

How to Replace Thermocouple On Gas Fireplace?

The thermocouple must be replaced when the pilot does not burn even after cleaning. This is a very easy and less time-consuming task. But you have to do the job diligently and efficiently.

 Before you go for the replacement, make sure that the thermocouple is fixed, just as you can replace the new one. If necessary, you can take a picture on your cell phone for visual reference. You can complete the task in three steps.

Step 1. Turn off the top line valve of your fireplace’s gas supply. Turn off the gas completely. To get the job done smoothly, give the thermocouple half an hour to cool down first. 

Buy a new thermocouple from the hardware store. Many styles of thermocouples are available. Collect the ones that are suitable for your fireplace from here. The tool that will do all this work is called a wrench. Collect this too.

Step 2. Unscrew the connector holding the thermocouple to the gas valve, then unhook the probe from its clip and carefully pull the whole thermocouple assembly. Before doing this, you must turn off the line valve on the gas supply.

Now replace the new thermocouple with a probe. Fix an investigation back to the clip. Keep it at the right distance from the pilot flame and screw the other end into the gas valve.

Step 3. Now illuminate the pilot and make sure the flame is burning. If the flame does not burn or does not last long, move the probe a little closer to the flame.

How Do You Know if Your Thermocouple Needs to Be Replaced?

If your gas fireplace will not stay lit, it is likely that your thermocouple needs to be replaced.
You can replace your thermocouple yourself. However, you should always consult your gas fireplace manual before performing any maintenance or repairs. You can find replacement thermocouples at most hardware stores or online.


You can replace thermocouples very easily and at a low cost. However, before you replace your thermocouple, make sure that it is not working properly even if you have cleaned it.

In this article, we have discussed how to clean a thermocouple in a gas fireplace and if necessary we have tried to tell you about the steps to replace it. If you think it’s still not working well, it’s best to call a technician.