How to Clean a Thermocouple in Water Heater (4-Step Guide)

Last Updated On June 12, 2024

Updated on April 20, 2023



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how to clean thermocouple on water heater

Is your pilot light going out unexpectedly? A dirty or malfunctioning thermocouple may be the culprit. If the thermocouple is malfunctioning, then it needs to be replaced.

But if it’s only dirty, then it can be cleaned and put back into service. So how do I know whether I have a bad thermocouple, or it’s only dirty?  

In this PlumbingNav guide, we’ll help you figure out which it is. And if it’s dirty, we’ll show you how to clean it.

What's In This Guide?

      Understanding a Water Heater Thermocouple

      A thermocouple is an electrical sensor. Two wires on one end connect to a thermometer on the other end. This acts as a safety device by shutting off the gas to the water heater when the pilot light goes out.

      The thermocouple generates a small electrical current when it comes into contact with heat (the flame from the pilot). This electrical current keeps the gas valve open so the gas supply can flow.

      When the pilot flame goes out, the electrical current disappears, causing the gas valve to close. A simple device designed to keep you safe.

      So a thermocouple in good condition is very important.

      Before You Clean: Verify the Thermocouple is the Problem

      How do you know that your thermocouple needs cleaning? 

      One easy way to determine if you have a bad thermocouple on your hot water heater is to pay attention to what happens when you light the pilot.

      If the pilot lights, but goes out when you let go of the ignition button, the thermocouple is likely to blame. The thermocouple isn’t keeping the gas valve open.

      If the pilot light won’t ignite at all or it lights for extended periods, and then goes out, the thermocouple is likely not the problem.

      If you think the thermocouple is the problem, it might need cleaning. Or it might need replacing. You’ll need to test it after it’s removed.

      How to Remove and Clean a Thermocouple on a Water Heater

      Here is a simple step-by-step guide on how to remove and clean your gas water heater’s thermocouple. 

      Caution: You will be working with gas lines that are under pressure. If you don’t have the training or experience with this, you should consider calling a professional.

      Check out this video on how to clean a thermocouple:

      First: Gather these supplies:

      • Wrench
      • Sandpaper
      • Cloth
      • Screwdriver
      • Multimeter
      • Owner’s Manual

      Caution: When purchasing cleaning supplies, avoid anything that contains chemicals. Stay safe and avoid these types of cleansers. Only use a mixture of soap and water.

      Step 1: Turn Off Gas

      Before working on a hot water heater, the first step involves turning off the gas. This ensures you will stay safe while you clean the thermocouple. 

      Get into the habit of turning the gas off every time you perform maintenance or repairs on your gas water heater.

      Look for a shut-off valve on the gas pipe near the water heater. You need to shut-off the gas flow with this valve. You also have the option to shut the gas off to the entire house from the outside.   

      Then, locate the gas control valve on your gas water heater. In most cases, the gas valve sits at the bottom of the unit. Turn the valve 90 degrees to turn the gas off.

      Step 2: Detach the Burner Assembly

      To properly access the thermocouple, unscrew the burner plate. You will need to disconnect the wires attached to the control center. 

      It’s connected in three places- the thermocouple, the main supply tube, and the pilot supply tube.

      The small copper wire is the thermocouple. At this time, you should be able to remove the burner assembly and access the thermocouple.

      FYI: We suggest taking a picture before detaching the burner assembly to help you reattach it properly. You can also use the owner’s manual. 

      Step 3: Testing the Water Heater Thermocouple?

      Now that it’s removed, let’s test it. You’ll need a multimeter.

      Set the multimeter to read for “ohms”. Take two leads from the meter and touch them together. They should read “0”. Now, set the meter back to volts.

      Next, get the thermocouple hot by putting an open flame to it. Once hot, connect the leads of the multimeter to the thermocouple.

      Your thermocouple should provide a reading between 25 and 30 millivolts. If it registers less than 25 millivolts, you need a new thermocouple.

      FYI: When buying a replacement for your thermocouple, keep the original and present it to your local supply store. This is important because the model number might not be visible or available. 

      You can also get a universal thermocouple. This will make your job easier. However it will affect the performance of your water heater, so we suggest you replace it with genuine parts whenever possible.

      If it passes the test, it’s time for cleaning.

      Step 4: Clean Thermocouple Thoroughly

      The main problems with the thermocouple include sediment build-up on the thermocouple itself and corrosion at the connections.

      To clean the sediment buildup, you will use sandpaper. Steel wool can also be used, along with a clean cloth.

      Clean the corrosion or rust between the control center and power wire.

      Make sure to clean any corrosion and rust between the control center and power wire. And only use soap and water. 

      You now have a clean thermocouple and burner assembly.

      did you know how to clean thermocouple on water heater

      Replace the Burner Assembly

      Now that the thermocouple is clean, replace the burner assembly. First, reattach the gas supply to the pilot. Next, you will screw the cover back on. 

      FYI: You can use the picture you took earlier or use the owner’s manual if that’s easier. Ensure all connections are tight.

      Reignite Pilot and Check Water

      Now you’re ready to reignite the pilot light on your water heater. To do this, you will turn the indicator to “pilot” and press the ignition button. Once the flame ignites, and you have held the button for 30 – 60 seconds, move the indicator to “ON”.

      Check the water to ensure it runs hot after about 1 – 3 hours, depending on your water heater. If the water heater is working again, great. If not, you may need to replace the thermocouple.

      Working with gas lines

      Natural gas lines are under pressure. This can cause some problems with the thermocouple, even if thoroughly cleaned or new. 

      Moisture might collect in the gas line. When you reattach it to the water heater, that moisture will contact the thermocouple causing it to shut off the igniter. 

      The solution is to clean the gas line by draining it and then drying it with a hairdryer. Then slowly increase the gas pressure by turning on the gas shut-off valve.

      As we’ve said, if you are not sure about working with gas lines, you should call a professional plumber. Better to be safe than sorry.

      When In Doubt-Call a Plumber

      At PlumbingNav, we want to guide you to complete simple repairs and maintenance yourself. However, at a certain point, you need to know when to step back and let a professional repair what you tried to fix.

      Dirty Thermocouple Water Heater FAQs

      Does My Water Heater Have a Thermocouple?

      Not all gas water heaters use a thermocouple. Some gas water heaters use a mercury sensor. Check your owner’s manual to find out which one you have. And if you have an electric water heater you will not have a thermocouple.

      How do I know if my thermocouple is bad on my water heater?

      The first sign of a problematic thermocouple is that the pilot light won’t turn on. This does not mean that the pilot light won’t ignite at all. That’s a sign of a different problem (likely a blocked pilot tube).

      If the light turns on but goes out after you let go of the ignition button, you should suspect a problem with the thermocouple. This is different than a pilot light that blows out.

      Can water damage a thermocouple?

      Yes. However, before replacing the thermocouple after a flood or contact with water, you can try to dry it out.

      Detach the thermocouple and allow it to dry out. You may also want to try using a hairdryer on a low setting to dry it out.

      Reach the thermocouple after you allow it to get completely dry. If it still doesn’t work, you will need to replace it. 

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      About Plumbing Navigator

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      We write about “all things plumbing,” helping you navigate common questions, repairs, and the best plumbing products on the market.

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