Step 1: Determine the correct size and style of thermocouple for your water heater. Information, such as your model and serial number can help determine the correct replacement. Most heaters will work with a 24″ universal thermocouple.
Step 2: Close the gas supply off to the water heater.
Step 3: Remove the bottom plate concealing the burner door and slight glass.
Step 4: Disconnect the thermocouple, igniter wire, pilot tubing, and main burner supply.
Step 5: Disconnect the high limit, or temperature cut-off switch (TCO) wiring.
Step 6: Remove the screws holding the burner door in place. Then slide out the burner.
Step 7: Remove the thermocouple from the pilot assembly.
Step 8: Remove the old push fit adapter and replace it with the new one supplied with the thermocouple. Insert the new thermocouple into the pilot assembly.
Step 9: Reinstall the burner. Make sure the front of the burner goes into the slot or bracket at the bottom of the burner chamber.
Step 10: Reconnect the main burner, pilot tubing, and thermocouple. Start all connections hand tight to avoid stripping the threads.
Step 11: Reinstall the burner door and tighten the screws.
Step 12: Reconnect the high limit or temperature cut-off (TCO) wiring.
Step 13: Reconnect the igniter wiring.
Step 14: Turn the gas back on to the water heater, then relight the pilot.
Step 15: Fire the main burner. Test for gas leaks with a soap solution at the pilot and main burner connections. If you see or smell any gas, turn the gas off, and recheck your connections.