The Honeywell thermocouple safety device senses the heat from a standing pilot light. The Honeywell thermocouple is made with dissimilar metals joined at one end. When heated by the pilot light, the thermocouple creates a small voltage. If this voltage is not present, the gas valve will not allow gas to pass through. This safety precaution prevents a buildup of raw gas. The Honeywell thermocouple is a quality, relatively trouble-free thermocouple. Things You'll NeedNew Honeywell thermocoupleTurn the power off to the furnace. Remove the access panel to the burner section by removing the screws with a screwdriver. Slide the panel up and pull it off. The access panel usually is the upper panel. The bottom panel normally is the return air section. Locate the Honeywell thermocouple. It looks like a copper wire. One end is connected to the gas valve; the other end is mounted in the pilot light block. Usually, the pilot light block is mounted on a burner. Turn the gas valve off. Remove the Honeywell thermocouple. With a wrench, remove the fitting on the end that screws into the gas valve. Remove the other end, which is mounted in the pilot light block. Several methods can be used to mount a Honeywell thermocouple in the block. If it is a screw-in type, remove the fitting with a wrench. If it is a clamp-on type, loosen the screw on the clamp and slide the Honeywell thermocouple out. If it is a push-in type, pull the thermocouple out. Install the new Honeywell thermocouple. Honeywell has a universal thermocouple that works on most furnaces. The part is manufactured in different lengths. The kit includes the different common adapter fittings. Screw the Honeywell thermocouple back into the gas valve. Ensure the fitting is clean and dry. Screw the fitting in finger tight. Tighten with a wrench about a 1/4 of a turn. Mount the silver end of the Honeywell thermocouple into the pilot light block using the same method used to remove it. Turn the power to the furnace back on. Turn on the gas valve. Light the pilot light according to the manufacturer's instructions. Ensure the flame makes good contact with the Honeywell thermocouple and that it stays on. Replace the cover panel in the same manner in which it was removed. To avoid damage, do not overtighten the fittings on the Honeywell thermocouple.