Hi, i’m Vance and welcome to Repair and Replace! If your old furnace isn’t starting, then it could be a problem with the thermocouple. In this episode, I’ll show you how to clean
and how to replace it. If your furnace was installed before 1990,
then it’s likely a Standing Pilot furnace. Pilot lights are small flames that burn continuously and will ignite the main burner when heat
is needed. The Thermocouple is a safety device that monitors
the pilot light. When heated, it creates voltage, which opens the
gas valve only when its safe to burn. Without a flame the thermocouple will cool
down, voltage will drop and the gas valve will close. If the thermocouple fails or if it’s dirty,
it will prevent the main burner from lighting, even when the
pilot light is burning. To begin, you might need a socket wrench or
nut driver, an adjustable wrench and a piece of emery
cloth. Follow the gas line into your furnace. On the gas valve there should be a switch
that shows: on, pilot and off. If the gas valve only says On or off, then
you have an automatic ignition system. The small tube that comes out of the gas valve
will lead into the burner. This is the pilot assembly. Next to the pilot is the thermocouple. If the thermocouple is dirty then it won’t
warm up, and won’t produce enough voltage to open the
gas valve. Its best to try cleaning it first. Always be safe!!! Turn off the power, and shut off the gas Next set the gas valve to the off position. Now let the furnace air out for 5 minutes.
Make sure it has time to cool down. Use an adjustable wrench to disconnect the
thermocouple from the gas valve. If your thermocouple is screwed into the assembly,
then loosen the nut. Other models simply push in. Press the tabs and slide the thermocouple
out of the mount. Use a soft abrasive pad or emery cloth to
gently clean the outside of the thermocouple. Be careful not to scratch the coating. Next insert the thermocouple into the pilot
assembly. Now screw the thermocouple into the gas valve. With the thermocouple cleaned, relight the
pilot and test the furnace. Turn on the power, and then turn on the gas. Next set the gas valve to the pilot position. Hold down the bypass button to let gas
into the pilot. Keep holding the button and use a BBQ lighter to insert a flame over the pilot assembly. Once the pilot light is ignited, continue
to hold the bypass button for another 30 seconds to let the thermocouple
heat up. This will keep the flame burning. Next set the gas valve to the on position. Now set your thermostat to heat. The furnace should be running normally. If the burner doesn’t stay lit, then replace
your thermocouple with a new one. Match the thermocouple length. Standard lengths are 18, 24, 36 and 48 inches. Now check the millivolt rating. Most universal thermocouples will be in the
25 -35 millivolt range and will be compatible with most furnaces. Also try to get a thermocouple that has the
right mounting option. If you are unsure then bring your old one
into the store, as a reference. Hopefully this has helped you get your old
furnace up and running. If you liked this and want to see more tutorials and informational videos,
then subscribe to our channel. And if you need help, you can call or visit
an AMRE location to talk with our knowledgeable staff. Thanks for watching.