How to Replace a Water Heater Thermocouple or Flame Sensor

How to Replace the Thermocouple on an Electronic Ignition Water Heater

1. Remove the Burner Assembly Manifold Cover

   The combustion chamber of water heaters with electronic ignition is found behind a cover that is sealed with a gasket. To access the combustion chamber, you must remove the burner assembly manifold cover, which protects the chamber holding the burner supply tube, burner, electronic ignition, pilot, and thermocouple.

   Remove the fasteners securing the burner assembly manifold cover plate. Depending on the brand and model of water heater you have, the panel may be secured by nuts, screws, or specialty tamper-resistant fasteners such as #20 Torx-head screws.

2. Remove the Burner Assembly

   Grab the burner supply tube and push down slightly to free the manifold, pilot tube, and thermocouple connections.

   Gently remove the manifold/burner assembly from the burner combustion compartment. Take care not to damage the internal components. If the burner does not move easily, check around the base—there may be additional screws holding it down.

3. Remove the Cover Plate Gasket

   Carefully remove the old gasket from around the manifold cover plate if it is in good condition and you would like to reuse it. Otherwise, remove the gasket and plan to buy a replacement.

   Clean off the metal surfaces between the cover plate and the water heater.

4. Remove the Thermocouple

   Slowly and firmly pull and twist the old thermocouple from its mounting bracket. It should come out easily if you use firm pressure. Make sure you do not bend or deform the connection between the pilot and the thermocouple bracket.

   Remove the old thermocouple completely by pulling it through the rubber grommet seal from inside to outside, or through the opening in the burner assembly manifold cover. You can cut the old thermocouple to remove it, if needed.

   Tip

   Take the old thermocouple to the hardware, home improvement, or plumbing supply store to buy an exact replacement. Also buy a new gasket for the manifold cover plate, if you are replacing the old one. 

5. Install a New Thermocouple

   Insert the new thermocouple from the outside through the grommet or opening in the burner assembly manifold cover. Insert the thermocouple into its mounting bracket until it is fully seated or clicks into place.

   Position the thermocouple tip so that the pilot flame will envelop the top 3/8 to 1/2 inch of the thermocouple tip.

6. Reinstall the Burner Unit

   Place the burner in the combustion chamber and properly seat the unit.

   Install a new burner manifold cover gasket, or reinstall the old one if it is in good condition. Reinstall the cover assembly. Do not over-tighten the screws or fasteners.

   Finally, reconnect the gas control valve (see below).

How to Replace the Thermocouple on a Standing-Pilot Water Heater

1. Remove the Burner Assembly

   Once the pilot supply tube, burner supply tube, and thermocouple are disconnected from the gas control valve (see above), simply lift and remove the burner assembly from the bottom of the water heater.

2. Remove the Thermocouple

   Slowly and firmly pull and twist the old thermocouple from the thermocouple bracket. It should come out easily if you use firm pressure. Be careful not to deform any of the parts.

3. Install a New Thermocouple

   Insert the new thermocouple into the bracket from which you removed it until it is fully seated or clicks into place. Position the thermocouple tip so that the pilot flame will envelop the top 3/8 to 1/2 inch of the thermocouple tip.

4. Reinstall the Burner Unit

   Reinsert the burner in the combustion chamber and properly seat the unit. Reconnect the gas control valve (see below).

How to Reconnect the Gas Control Valve

For both electronic-ignition and standing-pilot water heaters: Once the new thermocouple is installed, reconnect the pilot, burner, and thermocouple (and electronic igniter for an electronic-ignition unit) to the gas control valve.

1. Reattach the Gas Tubes

   Reconnect the burner supply tube, pilot supply tube, and thermocouple to the gas control valve. The mounting nut on the thermocouple should be no more than 1/4 turn beyond hand-tight. On electronic-ignition units, also reconnect the Piezo igniter.

2. Turn On the Gas

   Open the shutoff valve on the gas supply piping. Turn the gas control valve to the ON position. For standing-pilot units, relight the pilot, following the manufacturer's instructions, before setting the valve to ON. Set the water heater thermostat to the desired temperature.

3. Test the Water Heater

   Check the main supply tube and pilot supply tube at the gas control valve for gas leaks by using a soap-and-water solution. Coat the fittings with soapy water and look for bubbles that indicate a leak. If a leak is found, tighten all gas connections and retest them with soapy water until no leaks are detected.