A gas shut off valve can be found in most modern gas appliances. They are designed to close the gas supply if the pilot light flame does not come on, or if it is extinguished for some reason. You will occasionally have to replace the gas shut off valve, or thermocouple, as it is also called.
If you cannot light your furnace, or if your pilot light flame is a bright blue, then your gas shut-off valve has failed. In order to replace the thermocouple, you will need to extract the old one and purchase a new device which can be used to turn the gas off in an emergency. Follow these steps to replace your gas shut off valve.
Step 1 - Find a Replacement Thermocouple
Finding a replacement thermocouple is not always easy. Gas furnaces require that all of the parts of the ignition are connected together. The components cannot work if any of the parts don't match up. Buying an unsuitable replacement part would mean the thermocouple may not be able to detect changes in the pilot light flame, rendering it useless. You can find the part number of your thermocouple from the owner's manual, or by contacting the manufacturer of your furnace.
Step 2 - Prepare the Furnace
Turn off the electricity and gas supplies to your furnace. Allow it to cool down. It could take a while, so you might prefer to do another task while you are waiting for the furnace to become cool enough to touch.
Using your wrench, remove the bolt on the access panel at the front and place it to the side. You should then be able to see inside the furnace. Locate the pilot light and the switch, which is usually found on one of the furnace burners.
Step 3 - Remove the Old Thermocouple
Find the gas valve and then the copper tubing that connects it to your gas shut off valve. It should be removed from the gas valve, as well as the thermocouple. You should then also remove the tubing that connects the gas valve to the pilot light. Use your screwdriver to remove the brackets holding the shut off valve in place, and then lift up the thermocouple. Discard it to the trash.
Step 4 - Add the New Thermocouple
Take your replacement gas shut off valve and fit it back into the bracket. Screw the bracket back onto the wall of the furnace. The thermocouple should be securely connected to the pilot assembly.
Replace the tubing between the thermocouple and the gas valve, and between the pilot light and the gas valve. Make sure that all of these connections are tight, and that the gas valve's connections are air tight. You can then replace the access hatch of your furnace and light the pilot light. Turn on the power supply.