Things You'll Need
3/8-inch open-end wrench
Installing a new thermocouple on a Weil-McLain boiler will keep the system running safely and prevent gas from entering the room without being burned off. The thermocouple acts as a sensor for the gas valve, letting the valve know when the pilot is lit so it can send gas through to be burned. If the pilot goes out, the thermocouple is supposed to trigger the gas valve to shut off. Installing a new thermocouple can be done in about an hour with just a few tools.
Turn off the circuit breaker to your Weil-McLain boiler at the breaker box and remove the screws that hold the front cover onto the boiler with a screwdriver. Take the cover off the front then turn the knob on the gas valve so it is facing toward the word "pilot."
Remove the screws on the burner cover with the screwdriver and lift the burner cover off the boiler. Loosen the copper-colored thermocouple nut with a 3/8-inch open-end wrench and take the nut off the valve.
Lift up the back of the burner and slide the burner out of the boiler. Unscrew the thermocouple from the burner assembly and discard it.
Screw the new thermocouple onto the burner assembly and place the burner back into the boiler the same way it came out. Verify that the pilot tubing is fastened to the gas valve and fasten the thermocouple nut to the valve.
Press down on the red button on the gas valve and light the pilot light while holding the button down. Continue holding it down for about a minute then release the button.
Verify that the pilot stays lit and turn the dial on the gas valve to "On." Reattach the cover plate to the boiler then turn the circuit breaker on for the boiler at the breaker box.
To avoid injury, always shut off the circuit breaker to your Weil-McLain boiler at the breaker box before attempting to install the thermocouple.