Your water heater’s Thermocouple is used as a safety device to shut off your gas flow if your pilot light is not working.
The Thermocouple looks like a probe and because of its design there are no repairable parts.
When the end of the thermocouple is heated to a certain temperature the metal switch inside will allow voltage to flow back to your gas valve. If no heat is present then it will restrict electricity from reaching the gas valve and shut down gas supply to your heater.
If the device is installed correctly and has good connections then it should either work or not work.
Testing
You can test the thermocouple by removing it and attaching a volt meter. You should see voltage pass through the probe when it is heated. If there is no movement in your meter while heating it with a lighter or torch then the device is bad.
Four out of 5 times when your gas heater will not run and your pilot light continues to go out it means you need to replace the thermocouple.
Replacing your Thermocouple
To remove the thermocouple you will need to remove a plate that attaches the line of the thermocouple to the housing of your water heater.
Next detach the thermocouple from the valve with an open end wrench not pliers or an adjustable wrench.
Now you can remove the thermocouple probe end from pilot light mount the with a wrench.
Next you need to measure the length of your thermocouple or take it with you to your local store to pick a replacement part.
Many stores will not carry a specific model thermocouple they will have generic ones that are sold by length. Some may have a listing of models from various manufacturers that the thermocouple will fit so bring your Water Heater Model number with you.
Replacing the thermocouple is the opposite of the steps for removal.
Insert the probe end first and tighten with a wrench.
Then attach the valve side of the thermocouple making sure that your line is routed correctly.
Finally install the mounting plate as necessary.
Testing your work
When you are finished you should read your owners manual for information on initial testing and operation of your water heater.
Your Water Heater should now work without problems however you should keep an eye on it for the next few days as you would any repair.