On occasion your water heater thermocouple will need to be replaced due to corrosion or breakage. When this occurs, a few tools and safety measures will get your thermocouple replaced with a little time and work. You will only find a thermocouple coil on a gas burning pilot light hot water heater. Electric water heaters heat the water by elements and therefore do not need the same sensor as a gas water heater.
Step 1: Familiarize Yourself with Your Water Heater
Depending on whether you have a newer or older water heater you may need a Philips or standard screwdriver. View the gas valves, where the burner unit is located, how the thermocouple is attached, and that you have appropriate clearance to work. Because you are working on a gas water heater, additional safety measures need to be adhered to as well. Thinking and acting safely before you begin will make your simple thermocouple exchange an easy task. Ensure you do not have any open flames from cigarettes or other things in the area while you are working on your water heater.
Step 2: Access the Thermocouple
Locate the shut-off valves for the gas line. Turn off both the valve that is near the water heater and the valve that is on the gas line. Open the two doors that are at the base of the water heater. Remove the burner unit by locating and loosening the pilot light, gas supply tubes, and connection for the thermocouple.
Step 3: Release the Thermocouple
When you have the burner unit free from the water heater use the appropriate screwdriver to loosen the screw that holds the bracket for the thermocouple. Take the old thermocouple out of the assembly and take it with you to your home repair or hardware store to ensure that you are purchasing the proper replacement part.
Step 4: Install Replacement Thermocouple
Install the new thermocouple into the burner unit. Be careful with the soft metal of the thermocouple that it does not crimp or crack. The proper placement for the thermocouple is where a half inch of the tip is heated by the pilot flame.
Step 5: Re-insert Burner Unit
Install the burner unit back into the water heater. The gas burner supply, pilot supply, and thermocouple connectors need to be tightened. When you are tightening the thermocouple, make sure to not turn more than 1/4 turn past finger tight.
Step 6: Test Water Heater and Finish
Turn on the gas valves. To check for leaks in the valves put some soapy water on the connections. If you see bubbles being blown in the soap then you have a leak in your connections. Tighten more if you do see bubbles forming. Use a butane lighter to re-ignite the pilot. Ensure that 1/2 inch of the thermocouple is in the pilot flame. Put the internal and external covers back on the water heater. Keep an eye on the system for a couple hours to ensure the pilot light is igniting and shutting off as expected.