Turn the gas cock knob located on top of the thermostat in a clockwise direction to the “OFF” position.
Turn the temperature dial located on the front of the thermostat in a counterclockwise direction to its lowest setting.
Allow a minimum of five minutes to pass for any lingering gas to dissipate.
Trace the three metal tubes from the bottom of the thermostat to where the tubes pass into the bottom of the tank. The metal plate through which the tubes pass is called the outer access door.
Pull the outer access door away from the tank.
Disconnect the three tubes from the thermostat. Each tube is secured to the thermostat with an integral connecting nut. Loosen the three connecting nuts with an open-end wrench until the nuts detach from the thermostat.
Hold the three tubes together and pull them out of the tank to access the burner assembly. The thermocouple is located within a bracket located underneath the burner.
Pull the clip that secures the thermocouple to the burner bracket off the bracket with pliers and slide the thermocouple out of the bracket.
Slide the new thermocouple through its mounting hole within the burner bracket and press the clip over the thermocouple to secure it in place.
Insert the burner assembly into the tank.
Tighten the three tubes onto the bottom of the thermostat.
Light the pilot by following the instruction label affixed to the side of the tank.
Position the outer access door onto the tank.