person relighting furnace pilot light

A furnace pilot light is a critical component that can cause the heat to stop working suddenly. The furnace won’t fire up or produce heat if the pilot light goes out. Not all furnaces contain pilot lights, however. Newer furnaces ignite the burners with electronic ignitions.

An extinguished pilot light is typically a minor issue. Several circumstances can cause the pilot light to go out and the furnace to cease operation. Often, the pilot can be relit by following a few simple steps. A pilot that continually goes out indicates that professional help is needed to resolve the issue.

What Is a Pilot Light?

A pilot light is a blue, gas-fueled flame that constantly burns inside a furnace. It is sometimes referred to as a “standing pilot.” The pilot light ignites the natural gas or propane in the furnace’s burner at the beginning of a heating cycle. The burner heats the air coming into the furnace, and the fan distributes the warm air to the home. If the pilot is out, the burner won’t ignite, and the furnace won’t produce heat.

Pilot lights are standard in furnaces manufactured before the 1990s—newer furnaces, especially those manufactured since 2010, use electronic ignition systems. Pilots are inferior to electronic ignitions; they waste gas and are less safe and reliable. If you are unsure if your furnace has a pilot, check the owner’s manual. If your furnace is ten to fifteen years old, it probably has an electronic ignition.

If your furnace contains a pilot light, the unit is likely old and nearing the end of its life. According to the U.S. Energy Information Administration, forced-air gas furnaces last fifteen to thirty years. If you’re having issues with an outdated furnace, your best bet might be replacing it with a new, reliable, efficient furnace. One benefit of a forced air heating system is that furnace installers can usually swap out the old furnace for the new one without making many modifications to the ductwork or other parts of the system.

closeup of pilot light in gas furnace
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Where Is the Pilot Light on My Furnace?

Open the furnace’s access cover. Look for the gas valve’s knob labeled “on,” “off,” and “pilot.” The large pipe running through the valve is the gas line. The smaller tube that leads to the burner is the pilot tube. The copper line running alongside the pilot is the thermocouple.

The pilot tube has a nozzle on the end where the flame burns. If the pilot is lit, you will see a blue flame from the pilot's nozzle in the burner. If there is no flame, the pilot is out and must be relighted. If the furnace's gas valve knob is only marked "on" and "off," the system uses an electronic ignition and does not maintain a standing flame.

furnace pilot light location illustration

Reasons Your Pilot Light Keeps Going Out

Pilot lights are designed to burn constantly, but some circumstances can cause a pilot light to extinguish and prevent the furnace from heating up. A pilot light that goes out one time might be a fluke. If the pilot light keeps going out, consider these common causes:

rusted and corroded furnace flue causing pilot light to go out

1. Airflow Issues

The pilot’s flame can be blown out like a candle. Strong drafts from the wind, leaky ducts, or improperly installed or sized flues can be enough to blow out the pilot. Improper airflow is another possible cause. Closed registers can create a vacuum effect that extinguishes the pilot.

faulty gas regulator outside of home

2. Bad Gas Regulator

A faulty gas regulator on the gas meter outside your house would affect your gas furnace and all the gas appliances in your home. Call the gas company if your gas dryer, stove, or water heater is not functioning either.

dirty furnace pilot light orifice

3. Dirty Pilot Orifice

A dirty pilot orifice, the opening that emits gas, impedes the gas flow and might be enough to make the pilot go out. If you can relight the pilot, assess the flame’s color and strength. The flame should be blue and robust. Yellow, red, and weak flames indicate a reduction in gas flow and possible issues with the furnace heat exchanger.

furnace pilot light thermocouple

4. Thermocouple Issues

The thermocouple is a safety device that monitors the pilot light and opens the gas valve to ignite the burners. If the pilot light goes out, the thermocouple closes the gas valve to prevent a gas leak. A faulty, dirty, loose, or misaligned thermocouple prevents the gas valve from opening and the burner from lighting.

Furnaces that have electronic ignitions instead of pilot lights don’t contain thermocouples; they use a different safety device called a furnace flame sensor.

gas shortage causing furnace pilot light to go out

5. Gas Shortage

A shortage in the natural gas supply or a decrease in pressure during peak consumption periods can cause the pilot light to go out. If your neighbors are experiencing issues with gas appliances, the gas supply is likely the cause.

How to Light a Furnace Pilot Light

Lighting your furnace’s pilot might seem intimidating, but it only takes a few simple steps. Be sure to follow the safety precautions. Gas is highly flammable and explosive. Of course, calling an HVAC professional to relight your pilot is justifiable if you are apprehensive about doing it yourself.

1. Turn off the Furnace and the Gas

Turn the furnace off with the switch that resembles a light switch. Remove the furnace’s access panel. Follow the main gas line to locate the box-shaped gas valve. Turn the valve’s knob to the “off” position. Wait five minutes for any residual gas to dissipate and for the furnace to cool before lighting the pilot. Built-up gas is an explosion risk.

2. Find the Pilot Tube

The pilot tube is smaller than the gas line and runs from the gas valve to the burner. Use a flashlight to locate the nozzle on the end of the pilot. Have a long barbecue grill lighter or fireplace match ready if your pilot light has to be manually ignited.

3. Set the Gas Valve to “Pilot”

Turn the knob on the gas valve to “pilot.”

4. Light the Standing Pilot

Automatic pilots automatically ignite by pressing the red reset button. Other pilots need to be manually ignited with a lighter or match. Hold the reset button or depress the valve knob, depending on the furnace model. While pushing the button, bring the lighter or match to the end of the pilot nozzle. Continue pressing the reset button for thirty seconds after the pilot lights to maintain gas flow and ensure the thermocouple heats up enough to open the main gas valve.

5. Set the Gas Valve to “On”

When the pilot stays lit, gently release the reset button and turn the gas valve knob to “on.” Replace the access panel, and turn on the furnace switch. If necessary, increase the thermostat’s temperature setting to get the furnace to kick on. The burners should ignite. If they don’t ignite, the thermocouple might not have heated up enough. Repeat the procedure, holding the reset button for forty-five to sixty seconds after lighting the pilot.

Important Points

  • If you smell or suspect a gas leak, turn off the main gas line’s valve, and call a professional.
  • Only light the pilot after turning off the gas and waiting for it to clear.
  • A tightly rolled piece of paper or a match held with a pair of pliers can be used to light the pilot if you don’t have a long lighter or match.
  • Call a professional if the pilot won’t stay lit after three attempts.
  • Do not attempt to fix a broken furnace yourself.
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Today, most furnaces use electronic ignitions instead of pilot lights. Electronic ignitions don’t maintain a standing pilot or have to be relit. If you happen to have an old standing pilot furnace, the pilot light might go out because of airflow issues, a bad gas regulator, a dirty pilot orifice, thermocouple issues, or a gas shortage.

You can attempt to relight the pilot, but call a professional if the pilot keeps going out. Depending on the issue and how much it costs to repair, consider upgrading to a modern furnace. New furnaces with electronic ignitions are safer and eliminate pilot light issues. In addition, new furnaces are more energy efficient and might even lower your energy bills.


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