How to Install a Furnace Thermocouple

A furnace thermocouple is an important safety device. It uses the heat of the pilot light to generate a small amount of power. The power generated is necessary to keep the gas valve open, so if the pilot light goes out, the valve automatically shuts off. Because this is a failsafe system, the gas line will be shut off if the thermocouple fails. When this happens, you should replace the thermocouple.

Things You'll Need

• Wrench

Instructions

1. Shut off power and gas to the furnace. There should be a shutoff valve on the gas line near the furnace. Power can usually be shut off through a switch installed on the case of the furnace. If your furnace does not have a switch, shut off power at the breaker or fuse box.

2. Open the access panel on your furnace. Many furnaces can be opened by lifting upward on the access panel, but some require screws to be removed. If you are unsure of how to open the furnace, refer to the owner's manual.

3. Loosen the nut that holds the thermocouple in front of the pilot light. Once the nut is loose, the thermocouple can be slid out of the bracket.

4. Disconnect the thermocouple from the gas control valve. You can find where it is connected by following the wire from the end of the thermocouple. Unscrew the nut that attaches the thermocouple.

5. Install the new thermocouple in the same way that you removed the old one. Screw both ends into place, taking care not to overtighten.

6. Power up the furnace and open the gas valve.

7. Light the pilot light. Make sure that the tip of the thermocouple is in the flame. If the thermocouple is working properly, the pilot light should stay lit.