Furnace Pilot Light Troubleshooting

Pilot lights are integral parts of furnaces.

Pilot lights are integral parts of furnaces.

Any gas furnace uses a pilot light to trigger the burners to heat your home. The pilot light is a small flame that is either lit manually and remains burning around the clock or is lit electronically via an igniter when the machine kicks on. Regular maintenance and troubleshooting are part of the upkeep on a furnace to ensure the pilot light remains functioning.


The tip of the pilot light where the gas comes out and ignites is a haven for collecting soot, grime and grit over the years. From time to time, this tip can become clogged with debris that blocks the flow of gas, resulting in a pilot light that won’t stay lit. As a general rule, a toothbrush or a small, stiff brush is enough to clean the tip. If you want to be thorough, turn off the gas to your furnace, completely remove the tip and soak it in degreasing solution, such as what is used to remove grime from stovetops. After the debris has been removed, the pilot light should remain lit on its own. For best results, clean the pilot light every few months to prevent it from becoming clogged.

Flame Adjustment

Flame adjusters control the size of the pilot light's flame. If the flame is too small, it won’t kick on the burners. Not all furnaces have a flame adjuster. If yours does (refer to your owner’s manual), it will either be a small bolt or a small screw near the pilot light itself. In most cases, there should be a label or sticker near the pilot light that clearly details which direction to turn the screw to adjust the size of the flame. If in doubt, make small adjustments to the screw/bolt and check the visible size of the flame while the pilot light is lit. Sometimes during regular cleaning, or due to vibration of the unit, this adjustment can accidentally be turned down, resulting in a flame that is too small.


Your furnace requires fuel to keep the pilot light engaged and the burners functioning. If there is a leak, if there isn’t any gas in the reservoir or the valve from the reservoir is turned off, gas will not arrive at the pilot light. Check to ensure your tank has plenty of fuel, if applicable. Then, check to ensure that all valves along the supply line are turned on. Finally, check for leaks. A visible smell of gas is one sign, but if you are in doubt, coat any pipe connections with a mixture of dish soap and water. If there are leaks, bubbles appear on the surface of the solution. Leaks need to be repaired immediately to avoid potentially catastrophic results.

Ignition Switch

If your furnace is an electronic model with an automatic ignition for the pilot light but it won’t light, there may be an issue with the ignition. To determine this, turn off the thermostat. For best results, turn it off at the breaker box and wait a few minutes to turn everything back on. Sometimes this resets the machine. After you turn the machine back on, listen and watch to see if the furnace kicks on and the ignition sparks. If your unit has a hot surface igniter, it should begin to glow to prepare to ignite the burner. If none of these things happens while power to the furnace is turned on, there is an electronic issue that needs to be assessed and repaired by a licensed professional.

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