Check Your Thermocouple if Your Furnace Won’t Turn On

Time: 1 hour

We know, it’s hot — you probably don’t want to think about your furnace, but the best time to check your furnace pilot light isn’t when it’s already freezing outside, especially if you have a malfunctioning thermocouple. (That’s a safety device that hooks to your furnace and turns the gas off if the pilot light goes out.) No fear — here’s how you can fix it.

What's in it for you?

  • A warm home when winter rolls around
  • Chance to check other furnace problems
  • Lowered risk of furnace failure later in the year

(Show me how)

Clean Your Thermocouple:

  1. Find the thermocouple. Safety first — Turn off your furnace if it’s not already off. You can usually find it in your basement or in a closet somewhere on the first floor. Grab a screwdriver and remove the panel that’s close to the ground. Using a flashlight, find the pilot light (a small metal tip) and its thermocouple (a copper-tipped rod located opposite the pilot light).

  2. Remove the thermocouple. Put on a pair of gloves to improve traction and unscrew the nut and bolt holding the thermocouple down. (If you’re not sure which way to turn, remember “lefty-loosey”).

  3. Wipe off any dirt or stains. A dirty thermocouple won't detect a pilot light’s flame — not good. Clean the thermocouple with an old rag (or wire brush for tougher spots). You want to get that copper cutie looking spot-free and brand new.

  4. Inspect the thermocouple for damage. Check out the sides, top, and bottom for any scratches or breaks in the metal. Don’t be afraid to go full Sherlock Holmes with a flashlight and magnifying glass. No damage? Great, you can put the thermocouple back in your unit and call it a day. But if the thermocouple is damaged, you need to replace it.

Replace Your Thermocouple:

  1. Buy a new thermocouple. Head to your local hardware store with your thermocouple in hand and ask someone which type you can replace it with. Don’t forget to pick up a few extra nuts and bolts to swap out in case your old ones don’t fit or were damaged as well.

  2. Install the new thermocouple. Place the new thermocouple in the bracket where the old one used to be and screw it in (righty-tighty this time). Make sure to tighten it slowly so it’s even with the pilot light. Add the new nut and bolt to the outside of the thermocouple to hold it in place.

  3. Make sure it works. Turn your furnace back on and crank up the heat — don’t worry, it’s not for long. Listen for the sound of the pilot light turning on. If it kicks on within 30 seconds, your job is done. If it doesn’t, it’s a good thing you have enough time to call a pro.

Pro Tip: Before completely replacing your thermocouple, try adjusting its position to center it in the socket. There's a good chance that a slight alignment issue is causing the problem.

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