Water Heater

How to Test Thermocouple on Water Heater?

How to Test Thermocouple on Water Heater?

Your water heater produces hot water, making it a crucial component of your plumbing system. To guarantee reliable and appropriate operation, it needs routine maintenance. It is important to inspect the thermocouple for damage and replace it if required. So, how do you test thermocouples on the water heater? To verify if the thermostat on your water heater is operating, turn on the pilot light or measure the voltage. Continue reading for a detailed, step-by-step procedure.

Why Is A Thermocouple Required In A Water Heater?

Natural gas can enter the home if the pilot light is turned off (or broken) and the gas valve is left open, placing you at risk.

After some time, the thermocouple may become broken or loose. You cannot cut off the gas supply even with the pilot light lit. The water heater cannot supply hot water due to a lack of gas. As a result, determining what is wrong with a thermocouple is critical for repairing it and keeping your water heater operational.

Is It Necessary To Perform Thermocouple Tests?

The thermocouple, a wire-shaped electrical device, is fitted into the gas control valve of the water heater and is heated by the pilot flame. The thermocouple’s capacity to convert heat into an unstable current at low temperatures allows it to limit gas flow. This is achieved by combining two conductors of varying sizes. Gas flow may remain if the thermocouple is bad and the pilot light goes off. As a result, dangerous amounts of flammable and deadly gas may accumulate.

Also, Read: How to Adjust the Temperature on Water Heater.

How To Test A Thermocouple On A Hot Water Heater?

Pilot Test:

Find the gas tank in your house. You can find it in the basement. The pilot light is controlled by a box with miniature black, red, and white dials. There will also be a metal pipe conveying the gas.

Typically, the rotary knob on the gas valve is prominently labeled. Select “Pilot” as the mode. Press the reset button on the machine’s top to turn on the pilot light. Disengage the thermocouple by holding reset for 30–60 seconds. Release the button to see if the pilot light stops.

This light should stay on when turned on and off. The thermocouple breaks when the light goes out. You can uninstall or reinstall it immediately to improve test reliability. Turn off the gas before rechecking the thermocouple. Turn the dial to “Off” to confirm the thermocouple is the problem.

Turn off the gas with the knob. Try following the metal tubing to the pilot light control. A little valve was added. Rotate the valve counterclockwise to cut off the gas. Turn off this light after 20 seconds.

Turn off this light if the gas is off. After 20 seconds, air will flow even if the flame burns. The dial and valve must be adjusted. The gas valve should be simple to install.

The noise is coming from the junction of the gas supply line and the Gas Control Valve. The gas valve and thermocouple may have failed. Only professionals have the necessary licenses to replace a gas valve. Replace your thermocouple if you hear clicking before 20 seconds.

Multimeter And Millivolts:

To detect if the thermocouple is broken, use a digital multimeter to inspect it. Remove the thermocouple from the water heater or heating system to inspect it.

A lighter is enough for the test. Connect the alligator clip of the multimeter to the thermocouple end facing the gas valve. Connect the thermocouple’s opposite end to its base.

Check that the meter is set to millivolts. A measurement of 100 millivolts is possible but highly rare. If the value falls below 25 millivolts, the thermocouple must be replaced.


You can ensure consistency in hot water delivery and personal safety by regularly examining the thermocouple on the water heater. The testing of a thermocouple is described above. Cleaning and inspecting your water heater regularly will help you do your job and keep your home running smoothly. Turn off the gas before making repairs to your water heater for safety and efficiency. Ask a reputable specialist if you have any questions.


How do I tell if the thermocouple in my water heater is broken?

Make sure the pilot light is switched on before purchasing a replacement thermocouple. The pilot light will likely go out due to a broken thermocouple or a faulty gas supply.

What is the most typical reason for thermocouple failure?

One main concern with bare thermocouple wire is that it oxidizes, dramatically altering its composition. This is related to the production of oxide scales on the thermoelement surfaces.

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About the author

Mobeen Shahid

Mobeen Shahid is a Mechanical Engineer with two years of experience in the HVAC industry. His passion is analyzing HVAC issues, and he works relentlessly to devise customized solutions. He has been in the industry long enough to know the ins and outs and ensures that areas are optimally heated, cooled, and ventilated.