Gas Fireplace Thermocouple: How It Works and How to Setup

Key Points:

  • Gas fireplace thermocouple is a small but necessary part that is connected from the pilot light to gas valve.
  • It ensures that the gas valve is open or close at the right time.
  • Proper installation and maintenance of the thermocouple can prevent many unwanted situations.

A thermocouple is a basic component in a gas appliance that has a standing pilot. Though an automated spark ignition appliance does not need a thermocouple, other than that thermocouple in a gas fireplace is needed to function properly.

So, how does it communicate with the gas valve and operate? Is it important to light the pilot light?

Thermocouples communicate with the gas valve through thermal or heat sensitivity. The thermocouple is one of the main reasons why sometimes pilot light will not stay lit. However, it is a very important part when it comes to the functioning pilot light.

How Does a Gas Fireplace Thermocouple W1ork?

A thermocouple works via heat sensitivity which engages with the valve through a modest electrical pulse.

The tip of the thermocouple sits just above the pilot light and senses the heat while the pilot light is burning. The flame of the pilot light generates a voltage that keeps the valve open.

On the contrary, when it senses that the pilot light is going out, its thermocouple will shift off the gas supply.  

A thermocouple ensures the safety of a fireplace and the condition of the fireplace is always should be checked.

How to Know that the Thermocouple is Not Working?

The most common sign that the thermocouple is failed is, the pilot light won’t stay lit.

As it is not the only problem, you cannot be absolutely sure by this sign. You need to check the pilot light properly to see if there is any other problem other than the thermocouple. Sometimes clogged gas tubes of the pilot light can be the reason not staying lit.

Also, check the thermocouple to find any sign of corrosion.  These problems are not that complex and you can easily fix them by yourself.

Is There Any Difference Between a Thermocouple and a Thermopile?

A thermocouple is a thermal sensitive part of a gas appliance, on the other side, a thermopile is a series of thermocouples attached which are interconnected.

That means you can say, any device containing a thermopile has a thermocouple. Electricity is generated by both of them but thermopile generates more electricity than a thermocouple. Because several thermocouples are working inside the thermopile.

Thermopiles detect temperature and radiation more accurately than a thermocouple.

How to Test a Thermocouple?

The accurate way to test a faulty thermocouple is to test it with a multimeter that has alligator clips.

As you begin, set the meter to DC millivolts. After that, set one clip to the thermocouple probe and another near to the gas valve tube.

Turn on the pilot light and let it burn for 30 seconds. If the reading is less than 25 mV then the gas fireplace thermocouple is faulty.

How to Adjust a Thermocouple in a Gas Fireplace

To adjust the thermocouple firstly, turn off the gas and look for the thermocouple probe under the burner. Then simply pull or push the probe according to the adjustment you want.

A thermocouple needs adjustment because the pilot flame should touch it at a certain level. Otherwise, the fireplace will not work. To regulate the flame at a perfect level you can effortlessly adjust the thermocouple.

How Long Does It Last on A Gas Fireplace?

Generally, a thermocouple can last up to years before you need to replace it.

If you install and maintain it properly it can last up to fifteen to twenty years. This is the reason you should call a professional to check everything on your fireplace. Trying to save money and doing it yourself can cost you in the long run with a shorter fireplace lifespan.

Reasons Why Thermocouple Go Bad

There are several reasons of thermocouples go bad. The most common three reasons are

1. The Thermocouple is Broken

Sometimes the thermocouple cannot detect the flame properly because it is burnt out or broken. So, it cannot give the signal to the gas valve as a result the fireplace does not function properly.

A thermocouple is not that expensive, so check this before any expensive part gets wrecked as well.

2. It Needs Cleaning

If you do not clean the fireplace every season dirt and soot residue will build upon every part of it along with the thermocouple. When the thermocouple gets dirty it blocks out the flame and again, the fireplace malfunctions.

If this happens, remove the thermocouple and clean it with a brush and place it again.

3. The Thermocouple is Not Lined Up

The thermocouple should be lined up correctly so that it can fully respond to its sensitivity. This is a problem where every part of the fireplace is okay but still malfunctions.

Calling a good professional gas fireplace technician can solve this problem in no time.

Gas Fireplace Thermocouple Voltage

Thermocouples for the gas fireplace as well as other residential gas appliances like water heaters or furnaces are made for 30 Millivolts.

The voltage of the thermocouple of the gas fireplace should always be between 25 to 30 millivolts. If it goes below that, the thermocouple is defective.

How Much It Costs to Replace a Gas Fireplace Thermocouple?

It will cost you around $150 to $250 if you are willing to replace the thermocouple with a professional.

It is best to call a professional in case of the gas fireplace. Because the safety of you and your family coheres with it. A slight mistake can create massive destruction. So, I do not suggest ‘do it yourself projects with the fireplace.


A thermocouple is a small part of a gas fireplace but plays a huge role in it.

So, make sure to inspect it often. It is best if you call a professional after every season and check the fireplace thoroughly. It ensures the longevity of the fireplace and the safety of your family.

A thermocouple is not an expensive part of the fireplace. So, replace it as soon as you see the signs of disturbance. Otherwise, it will harm the other parts of the fireplace as well.

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