Furnace Pilot Light Won’t Stay Lit After Replacing Thermocouple [Solved]

If your furnace pilot light won’t stay lit after replacing the thermocouple, we can help you solve it in less than an hour. This article will cover 5 possible reasons why your pilot light won’t stay lit replacing the thermocouple and how to fix the issue.

By the end, you will have a perfectly functioning furnace. You can also try these solutions if your Williams wall furnace or Honeywell water heater pilot light won’t stay lit as well. 

But, remember, this guide won’t effective when your furnace pilot light is lit but the furnace won’t ignite. In such a case, you can read our simple solution guide for pilot light lit but burners won’t ignite.

So let’s get started.

Furnace Pilot Light Won’t Stay Lit Replacing Thermocouple-Fix

It will be easier for you to solve the issue if you know why a pilot light won’t stay lit after replacing the thermocouple. 

The most common reasons for pilot light failure after replacing the thermocouple are dirty furnace parts, faulty gas valve, defective thermocouple, improper draft positioning, and incorrect installation of the thermocouple. Below you will find effective solutions to these 5 problems. 

1. Dirty Furnace Parts

The most common reason why your furnace pilot light won’t stay lit is dirty furnace parts. Replacing the thermocouple may only have little to do with this issue.

A dirty pilot burner and orifice prevent the pilot light from burning. When you replace the thermocouple, these dirty furnace parts may just attract more dirt to their delicate points, causing the pilot light to go out.


You can solve this issue just by cleaning these pilot burner parts. Here’s how to do it properly,

  • Remove the pilot tube first
  • Rub a piece of sandpaper on the tip of the pilot orifice
  • Use a can of compressed air in the points where dirt is most likely to accumulate
  • Use a thin, soft-bristled brush to reach every tiny nook of the orifice and burner

Now put the pilot tube back on.

2. Faulty Gas Valve

The gas valve is responsible for supplying gas to the furnace. It may fail to do so if the gas valve is faulty. And when the gas supply is hampered, the pilot light will not work as well.


Changing the gas valve is the best solution in this situation. Here’s how to do it,

  • Turn off the gas supply
  • Unscrew the valve using a wrench 
  • Clean the area if you notice any dirt accumulation
  • Install a new gas valve
  • Make sure the valve is tightly screwed in its place

Don’t forget to purchase the perfect-sized gas valve for your furnace before starting.

3. Defective Thermocouple

If the changed thermocouple is not working, then the thermocouple itself might be the culprit. A thermocouple basically works when a pilot light does. So a bad thermocouple will definitely cause the pilot light to go out.


You cannot avoid installing a thermocouple in your furnace. But you can prevent installing a defective one if you know how to recognize a good thermocouple. Well, if you don’t know how to do that either, then here’s how,

  • Keep a multimeter near your reach and set it to ‘Volts’. Make sure the reading is zero
  • Place the tip of the thermocouple near a burning flame
  • Keep the thermocouple there till it is hot
  • Place one lead of the multimeter on the shaft of the thermocouple
  • Place the other lead of the multimeter on the point where the thermocouple met the gas valve
  • Examine the reading

If the reading says 25+ millivolts, then that thermocouple is perfectly fine. So, do test the thermocouple this way before installing it.

4. Improper Draft Positioning

If your furnace’s pilot light goes out after a few hours, the problem is probably with the draft positioning. The draft’s position can get affected while installing the thermocouple in the furnace.

If this happens, excessive air will flow into the furnace, eventually causing the pilot light to go off. 


Just put the draft back in its position, and it will solve the issue. However, look for other potential paths that are likely to allow the circulation of airflow in the furnace. Close or seal that path if you find any.

In case the changed thermocouple still not working, try the next method. It will surely do it unless the whole furnace is broken.

5. Improper Installation

If none of the above-mentioned solutions work for you, then the reason can be the improper installation of the thermocouple. It is very easy to get it wrong as it’s a complicated task. However, we will show you how to install a furnace thermocouple easily.


Remove the thermocouple first and follow these steps to install it properly,

  • Make sure that the lead on the thermocouple is completely straight
  • Now shape it in a way that matches the structure of the thermocouple
  • Connect the thermocouple to the pilot burner assembly bracket
  • Connect the gas line and the gas valve to the pilot thermocouple
  • Screw all the nuts tightly on the gas valve

Now turn on the power of the furnace. Your furnace pilot light should burn just fine if you have got all these steps right. These solutions are also effective for the pilot light won’t stay lit on the gas water heater as well. 


Why does my pilot light go out when I release the pilot light knob?

If your pilot light goes out whenever you release the pilot knob, you need to replace the thermocouple.

What does it mean when your furnace pilot light keeps going out?

Furnace pilot lights keep going out can indicate broken thermocouples, dirty furnace parts, and an inconsistent supply of gas.

How do I know if my thermocouple is bad on my furnace?

The most common sign of a bad thermocouple is the flame going out after releasing the gas control knob.

How much does it cost to replace a thermocouple on a furnace?

Replacing the thermocouple with the help of an expert can cost more than $200. However, it can be done just with the price of the thermocouple ($75) if you follow our instructions.

Do you need to turn the gas off if the pilot light goes out?

No, you don’t have to turn the gas off if the pilot light goes out.


The pilot light is a crucial part of the furnace. This is why it is important to ensure that it’s working all right. But things can easily go wrong, especially after you make modifications. 

So if your furnace pilot light won’t stay lit after replacing the thermocouple, follow the instructions discussed in this article. It should solve your problems. However, if you face further difficulty, reach us by commenting below.

About William

William is the founder of Fireplacehubs.com. He has real life practical skills in fixing smoker & heating appliance issues. He loves to share his knowledge & helps others in fixing their appliances & saving their money. William firmly believes that anyone can repair his or her unit with the correct guidance & knowledge. See more at about us.

6 thoughts on “Furnace Pilot Light Won’t Stay Lit After Replacing Thermocouple [Solved]”

  1. replaced thermal couple lit pilot , Works well. When furnace turns off the pilot light goes out, Have to continually relite pilot. Played all tubing thoroughly still no help.

    • Hi Patrick

      Besides defective thermocouple, dirty furnace parts, faulty gas valves, improper draft positioning, and incorrect installation of the thermocouple are also the reasons behind the pilot light going out. Did you check all these issues? If not, check these to fix your problem.

      Hope you will get the solution.


  2. My thermocouple has been replaced and furnace has been running over 20 days but I just came home and the pilot is gone out again so I lit it again and it only stayed on properly 10 minutes and I heard it clicked off again…

      • So i figured out my issue, it was just the Thermocouple wasnt tightened enough. they say in all the videos and books to not tighten it and the pilot tube too tight, but i had to crank down on mine a bit and then it lit right up. so make sure your nuts are tight bois.


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