Remember to remove the knobs first.

Unscrew the screws located at the top and bottom of the water heater.

Gently remove the cover by sliding the cover up towards the top and mind the wires and the on/off switch.

Disconnect wires from the microswitch/solenoid and unscrew the battery box ground wire from the gas flow dial base.

Disconnect wires from over temperature sensor using pliers.

Unscrew the water flow pipe from the assembly. Unscrew the assembly from the gas pipe.

Unscrew the assembly from the back of the unit.

Slide out the assembly at an angle to avoid getting inlet and outlet pipes caught. (This might take some maneuvering)

Slide in new assembly and screw assembly back to gas and water pipe.

Screw the assembly back into the base of the unit, reconnect all wires, and put the cover back on.