If you heat your home with natural gas, oil or propane, chances are your furnace or boiler has a pilot light. With the help of two experts Joshua Smith from Berkshire Heating and Cooling and Alexander Siv from Amherst Plumbing and Heating learn what a pilot light is, some reasons it may go out, and what to do if it does.

What Is the Pilot Light on a Furnace?

A pilot light is a small flame that’s constantly lit within a gas furnace. It’s the ignition source for the main gas burner when it’s activated by the thermostat. Other gas appliances like stoves, ovens and water heaters may also have pilot lights.

Electric furnaces do not have a pilot light. And starting around 2010, gas furnaces haven’t, either.

“Pilot lights are an older technology,” Smith says, “Modern gas furnaces use a hot surface ignition source that relies on electricity.” But there are still plenty of pilot light ignition systems still in use.

What Causes the Furnace Pilot Light To Go Out?

There can be several reasons why your pilot light is out:

Faulty thermocouple: A thermocouple is a temperature detecting device that works with the pilot light to control the gas valve. If the thermocouple breaks, the gas valve will close, snuffing out the pilot light. Smith says this is the most common cause of the problem.Broken gas valve: “Sometimes the gas valve itself fails and stops releasing gas, which can also cause your pilot to go out,” Siv says. Smith cites this as the second most common cause.Wind blows it out: “If there’s a crazy storm with high winds, it can blow out the pilot,” Smith says, “But it’s unusual.”

How Can I Tell if the Pilot Light on My Furnace Is Out?

You’ll need to do a visual inspection. Consult your furnace owner’s manual to determine the pilot’s exact location. Most are near the bottom of the furnace, behind a removable access panel.

Take off the panel and look for a small bluish flame. If there’s no visible flame, your pilot’s out.

Here’s another obvious sign: You turn up the thermostat but your house stays cold. “You’ll have no heat because the pilot’s not there to ignite the burner,” Smith says.

Does Gas Still Flow When the Furnace Pilot Light Goes Out?

No. The thermocouple will stop detecting heat and shut off the gas valve.

Can I Relight the Pilot Light Myself?

It depends. “Anyone can relight a pilot,” Siv says, “but the reason your pilot light went out in the first place will determine if it’s able to be relit.”

If it’s due to a bad thermocouple or gas valve, these will need to be repaired first. Also, if the pilot light orifice is clogged, it will need to be cleaned before relighting will be successful.

The pilot lighting instructions should be right on the equipment. If you’re not comfortable relighting your pilot, call an HVAC pro to do it for you.

How To Relight the Pilot Light on a Furnace

If you know why your pilot light is out, and you feel confident in your skills and abilities, here are steps to relight a pilot light. Make sure to consult with your furnace’s owner’s manual for more detailed instructions.

Turn off the thermostat.Turn off the power to the furnace by flipping the breaker.Wait 10 minutes for any gas to dissipate from the line.Remove any control panels from the side of the furnace. These often simply lift off.Locate the pilot light control knob. This usually has ‘On,’ ‘Pilot’ and ‘Off’ printed on it.From the knob, follow the gas line (a thin metal tube) to where it ends. This is where you hold the flame to relight. It’s called the flame deflector and is usually L-shaped.Turn the control knob to ‘Pilot.’Press and hold the starter button, usually next to the control knob. This opens the gas valve.Light a 12-inch match or 12-inch barbecue lighter. Hold the flame near the open end of the flame deflector.A flame should appear and stay lit after you remove the match or lighter flame.Continue to hold the starter button for about 30 seconds. “This allows time for the thermocouple to engage and keep the gas valve open,” Siv says.Release the starter button.Turn the control knob to ‘On.’Watch the flame for a few minutes to ensure it stays lit.

If the flame doesn’t stay lit or needs to be manually relit often, Siv says this indicates a mechanical problem with the thermocouple or gas valve. “It’s best to call in a pro at that point,” he says.

About the Experts

Alexander Siv owns Amherst Plumbing and Heating in Amherst, Massachusetts. He has a master plumber’s license in Massachusetts and more than 10 years of plumbing experience.Joshua Smith is operations manager at Berkshire Heating and Air Conditioning in West Springfield, Massachusetts. He has more than 20 years of HVAC experience and holds a Massachusetts oil burner and refrigeration license.Read More