Water Heater Pilot Light Won’t Stay Lit After Replacing Thermocouple? 5 Fixies

The water heater pilot is an essential element in your water heater, as it is the connection between the gas valve and the burner.

Basically, a functioning water heater pilot will ensure that there is a constant flame lighting the burner.

As for the water heater pilot light, it indicates that the water heater is on and functioning properly.

That being said, if your water heater pilot light won’t stay lit after replacing the thermocouple, this could indicate a few different issues that we’ll discuss in this guide, as well as the best solutions!

Why won’t the water heater pilot light stay lit after replacing the thermocouple?

Many people choose to simply replace the thermocouple when experiencing problems with their water heater pilot light.

However, what happens if the issue persists even after you’ve installed a brand new thermocouple?

Here are some of the most common core issues behind a faulty water heater light.

1. Faulty gas control valve

The gas control valve has a very important role in the functioning of the water heater, as it manages the gas flow from the gas inlet.

If the gas control valve is working properly, you will be able to use it to ignite the pilot, which will then heat the thermocouple.

Once the thermocouple in the water heater has reached an adequate temperature, it will send a signal back to the gas control valve, which will enable the burner.

Once the burner is turned on, the water in the tank will start heating up.

However, if the gas control valve is damaged or simply not working properly, this will affect every stage of the process and all the components, including the water heater pilot.

If the water heater pilot won’t stay lit even after you’ve replaced the thermocouple, this could mean that the gas control valve can’t open up and release the gas.

2. Faulty thermal switch

The thermal switch, also known as the thermal cutoff (TCO), thermal limit switch and temperature sensor, is connected to the thermocouple and it is mainly a safety feature.

It is able to detect flammable vapors, protecting the water heater from excessive electricity flow and damage.

In case the water heater pilot light doesn’t stay lit, it is possible that the thermal switch is either damaged or tripped.

3. Faulty thermocouple

Even if you’ve replaced the thermocouple, it is still possible that the thermocouple is not functioning properly.

You can easily test this possibility by simply lighting the water heater.

In case the pilot light shows up and then disappears after you release the knob, this means that the problem concerns the thermocouple or another electrical component.

You can also troubleshoot the thermocouple by testing its voltage with a multimeter.

In case the multimeter shows less than 20 millivolts, the thermocouple isn’t working properly.

4. Clogged pilot tube

The pilot tube includes an opening called the pilot orifice, which needs to remain clean and obstacle-free in order for the gas to flow freely.

However, a common problem with the pilot tube and the pilot orifice is that it gets clogged with dirt and gunk, jeopardizing the entire unit and affecting the pilot light.

Luckily, it is rather easy to get rid of the clog and fix this problem, which we’ll get to in the next section.

How to fix a water heater pilot light that won’t stay lit after replacing the thermocouple

Now that we’ve listed some of the most common issues causing the water heater pilot light to act up, we can proceed to the most important part: the solutions.

As you already know, troubleshooting your appliance and detecting the core issue is crucial.

It will save you a lot of time, energy and money when fixing your water heater pilot light.

1. Repair or replace the gas control valve

In case the thermal switch and the new thermocouple don’t seem to be the issue, it is possible that your gas control valve is damaged or malfunctioning.

A bad gas control valve can be quite dangerous and cause many serious issues with your water heater.

That being said, we recommend contacting a professional to either repair or replace your gas control valve.

Tending to this matter yourself, especially if you have no experience, isn’t advised.

2. Fix or replace the thermal switch

As we’ve explained in the previous section, a thermal switch is a very important element in your water heater system and a crucial safety feature.

A common issue with the thermal switch is that it trips and disables the gas control valve due to a blocked air inlet screen or vent.

What you should do in this case is find the cover at the bottom of the water heater and then remove it to access a small button between the two switch terminals.

Press the button until you hear a click and then attempt to relight the pilot.

Check if the pilot light stays lit after pressing the button.

It is also necessary to perform the continuity test across the two terminals by disconnecting the wires from both of them. 

Adjust your thermometer to the lowest setting of resistance.

Then, position the multimeter probes on the two thermal switch terminals.

If the pilot light passed the continuity test, this means that the thermal switch was tripped and is now functioning properly.

However, a negative continuity test indicates that the thermal switch is faulty and should be replaced. 

You can easily replace the thermal switch by disconnecting the old thermal switch from the tank using a screwdriver. 

Simply pull out the faulty thermal switch and connect a new one using the same wires.

You can always take a picture of the old setup before you remove the thermal switch for reference. 

3. Reposition the thermocouple

Just by slightly bending the new thermocouple you’ve installed; you can solve the issue of the water heater pilot light that doesn’t stay lit.

You first want to remove the cover at the bottom of the unit to reach the pilot light.

Try relighting the pilot, and once the pilot flame appears, hold the gas valve button for about a minute.

As you’re pressing down the gas valve button, take the thermocouple wire and make a slight bend, making sure not to damage it. 

You can now release the button and check if the pilot light is working properly.

If this trick worked, it could be that you haven’t positioned the thermocouple properly in the first place or that it is faulty and should be replaced in the near future to avoid similar issues. 

4. Unclog the pilot tube

As we’ve mentioned, it is quite common for the pilot tube to get clogged with gunk, which could disrupt the gas flow, as well as the functioning of the pilot light.

You can unclog the pilot tube in just a few simple steps.

Under the access cover, there should be the pilot orifice, which you have to unscrew by twisting it to the left.

Take a cotton swab and wet it with some rubbing alcohol.

Then, use it to reach all the areas of the pilot tube, making sure to remove as much gunk as possible.

You may also use a toothpick for tighter areas.

Once you’ve cleaned the pilot tube and its elements, put everything back into its initial position.

Try relighting the pilot by holding down the control knob while lighting the pilot with a long match or wand lighter. 

Once the pilot ignites, it is necessary to still hold the control knob down, which will release any excess air from the pilot tube, ensuring that the gas flow is smooth.

Make sure to check if your pilot comes with an automatic igniter since these models do not require a match or lighter to ignite. 

5. Re-install the thermocouple

In case the thermocouple bending trick didn’t work for you, or it didn’t give any permanent results, it could be that you haven’t properly installed the thermocouple.

In this case, the only solution would be to re-install the thermocouple and ensure everything is properly positioned and connected before attempting to relight the pilot.

When installing the thermocouple, one of the most important steps is to ensure that the thermocouple lead is completely straight; otherwise, it won’t function properly.

You also want to make sure its shape matches the actual structure of the thermocouple.

Now you want to connect the thermocouple to the assembly bracket of the pilot burner.

A common mistake people make when installing a new thermocouple is mismatching the gas line and gas valve connections.

Make sure to properly connect both of these lines to the pilot thermocouple.

The final step when installing the thermocouple would be to secure the gas valve tightly using screws. 

Now that you’ve gone through all the necessary steps of installation, you can test the water heater pilot light by trying to reignite the pilot.

If it stays lit, it means that you’ve successfully solved this issue and re-installed the thermocouple. 

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