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How To Clean A Thermocouple

How To Clean A Thermocouple

If you are asking questions like "How do you clean a thermocouple?", chances are you are not the average fireplace owner. Some people have trouble pronouncing that word, much less learning how to maintain it. So, this article will not be basics about cleaning a gas fireplace. This is an in-depth look at gas fireplaces, their parts, and how to maintain them. If that sounds like something you need, keep reading, we promise to make it as pain-free as possible.

How To Clean A Thermocouple

Many gas fireplaces use a standing pilot or millivolt valve as a part of the way they ignite the main burner. Though it might seem like a magic fairy sits behind the wall switch connected to your fireplace and that is what makes the fire roar to life... sadly, that is not the case. A small probe called a thermocouple, or thermopile is heated through a small standing flame.

How To Clean A Thermocouple

Thermocouples operate when two different types of metal inside them are heated and create a small amount of voltage. A thermocouple actually creates a little less voltage than a thermopile, but don't give it too hard of a time, it tries its best. The voltage that is created when the metal is heated travels down a copper lead to the gas valve that controls the appliance. Then that voltage charges a small electromagnet in the valve which holds it open and allows for gas to flow. And voila, magic without all the pixie dust!

Over time, it is common for soot to build up on the surface of the thermocouple, because it cools rapidly even as the flame touches the surface. That causes incomplete combustion and everyone is sad. Thankfully, many thermocouples can go years before this buildup leads to improper function of your fireplace. One quick way to find out if your fireplace isn't turning on because of a dirty thermocouple is to look at the pilot assembly and see if the pilot light is still burning. If it isn't, the thermocouple is dirty and there will be no magic fairies coming to clean it for you. So, hop to it!

How To Clean A Thermocouple

To begin the cleaning process you'll need to wait at least 20 minutes for the unit to cool if it has been burning recently. Next, turn off the gas to the appliance & unplug anything connected electrically just to make sure nothing sparks while you are working on the thermocouple. Remove the glass or any screens covering access to the pilot burner assembly. It also may be a good idea to take photos as you do this to ensure you know how to put everything back on when you are done.

How To Clean A Thermocouple


Once all that is complete, use a thin strip of emery cloth or 320 grit sandpaper to polish the thermocouple & remove soot. When the probe has become semi-shiny, your work is done. It would be smart to use compressed air to blow out any leftover debris after you are done polishing. Before re-installing the gas logs, turn on the gas and relight the pilot assembly. Because air will be in the system, it may take a few attempts for it to light again. Don't worry. That is totally normal.

One last thing to take note of is the flame appearance in the pilot. It should be blue and engulf the upper third of the thermocouple. If the flame happens to be yellow and engulfing the lower portion of the probe, you done messed up. Kidding! That means the air intake holes in the pilot assembly also need cleaning. Sigh.

How To Clean A Thermocouple

You can clean them by poking a piece of fine wire into the holes or spraying them with compressed air — which you should obviously do only when the gas is turned off and everything else is unplugged again. After cleaning the air intake holes, light the pilot again and check the flame a second time. If the flame is strong and blue but not centered on the thermocouple, you can adjust the thermocouple by sliding it forward or backward in the pilot bracket. Keep in mind this is only possible for models that have a thermocouple that sits horizontally above a pilot.

How To Clean A Thermocouple

When all of those steps are complete, light the pilot & let the flame burn for about a minute before you try to turn on the main burner. If the main burner does not turn on but the pilot light is working, most likely the thermocouple has failed and you need to replace it. If you need help with that you can call our NFI certified techs any time at 800.203.1642 to help you find the correct parts for your gas fireplace. We hope this article has been informative and given you everything you need to approach these task with ease. If you just love reading about fireplaces, you can nerd out over our article library here:

About the Author

Collin Champagne

With over 13 years in the industry, Collin is a National Fireplace Institute (NFI) certified technician and managed content for the eFireplacestore and eCanopy brands. He has achieved the highest NFI certification possible as a Master Hearth Professional and is certified in all three hearth appliance fields: wood, gas, and pellet. With experience with sales and in-field installations, his expertise shines through his technical knowledge and way with words.

Customer Q&A with Product Specialists

Joseph Y. from TN asked:
My pilot light is working perfectly.  I can finesse the burner to light, but only for a moment, and the pilot goes out, and then the burner stops working. I have clean out all the lines and fittings. Could this be the thermocouple? Is there a way to bypass the test?
My pilot light is working perfectly. I can finesse the burner to light, but only for a moment, and the pilot goes out, and then the burner stops working. I have clean out all the lines and fittings. Could this be the thermocouple? Is there a way to bypass the test?
Your thermocouple is possibly not recognizing the pilot flame, which is causing it to go out. You will want to clean the thermocouple with a piece of emery cloth or high grit (1000) sandpaper. This may resolve the issue. Another issue that could be causing this is the connection point between the thermocouple lead and the gas valve. Depending on your fireplace, there may be either a pair of lead wires or a solid copper lead that is held in place by a nut. Either way, loosening and cleaning the connection point at the gas valve will often make a difference, as excessive voltage drops can occur at this location and cause the pilot to drop out.  If that does not work, you can use a multimeter to test the millivoltage to see if there is an issue there.
Answered by: on Jan 11, 2024


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