The basic steps to relight your furnace
To light a gas furnace pilot light, turn the gas control knob to "Pilot," hold down the ignition button while holding a lit match or lighter to the pilot opening, and keep the button pressed for 30 to 60 seconds after the flame catches. Once the pilot stays lit on its own, turn the knob to "On" and listen for the main burner to ignite within a minute.
The exact location of the pilot light varies by furnace model — it is usually inside the combustion chamber at the base of the unit, sometimes behind a small access door or panel. Check your furnace manual or look for a diagram on the unit itself to find where the pilot opening is on your specific model.
If the pilot will not stay lit after you release the button, or if it lights but the main burner does not ignite, the problem is usually a faulty thermocouple (a safety sensor) or a gas supply issue. These require a technician to diagnose and repair.
Key Takeaways
- Turn the gas control knob to "Pilot," press the ignition button, and hold a flame to the pilot opening until it catches and stays lit on its own.
- Keep the ignition button pressed for 30 to 60 seconds after the pilot ignites to allow the thermocouple to heat up and signal that gas is safe to flow.
- Once the pilot is lit, turn the knob to "On" and wait for the main burner to ignite within one minute.
- If the pilot will not stay lit or the main burner does not ignite, the thermocouple or gas line may need professional inspection.
Finding the pilot light on your furnace
The pilot light sits inside the furnace's combustion chamber, but the exact spot depends on your model. Most furnaces have a small access panel or door near the base where you can see or reach the pilot opening. Some units have the opening visible without removing anything; others require you to unscrew a small cover plate.
Before you start, turn off the furnace at the thermostat and wait five minutes for any residual gas to clear. Then locate the gas control knob — it is usually a dial or lever on the side of the gas valve, marked with "Pilot," "On," and "Off." Your furnace manual or a label on the unit itself will show you exactly where to look.
If you cannot find the pilot opening or the gas control knob, do not force anything. Take a photo of your furnace model number (usually on a label near the top or side) and search the manufacturer's website for the manual, which will include a diagram.
Turning the knob and pressing the ignition button
Turn the gas control knob all the way to "Pilot." This setting allows gas to flow only to the pilot, not to the main burner. You should hear or feel a slight click as the knob moves into position.
Next, locate the ignition button — it is usually red or black and sits near the gas control knob. Press and hold it down. You may hear a clicking sound as the igniter sparks, or you may not hear anything if your furnace uses a piezo igniter (which makes a very faint sound). Keep holding the button while you bring a lit match or lighter to the pilot opening.
Hold the flame close to the opening for a few seconds until you see the pilot flame catch. The flame should be blue with a small yellow tip. Once it ignites, keep holding the ignition button down for another 30 to 60 seconds — this allows the thermocouple to heat up and signal the gas valve that it is safe to keep the pilot running.
Releasing the button and switching to "On"
After 30 to 60 seconds, slowly release the ignition button while watching the pilot flame. If the flame stays lit, you have succeeded. If it goes out when ready, wait a minute for the furnace to cool slightly, then repeat the process — sometimes the thermocouple needs a second attempt to heat up fully.
Once the pilot is holding steady on its own, turn the gas control knob from "Pilot" to "On." This opens the gas line to the main burner. Within 30 seconds to one minute, you should hear a whoosh sound as the main burner ignites. The furnace will then begin heating.
If the main burner does not ignite within a minute, turn the knob back to "Off" and wait five minutes before trying again. Repeated failed attempts suggest a problem with the gas supply or ignition system that needs professional attention.
What to do if the pilot will not light
If you cannot get the pilot to ignite at all, first check that gas is actually reaching the furnace. Smell near the gas control knob — natural gas has a distinctive rotten-egg odor added to it for safety. If you smell gas but the pilot will not light, the igniter may be broken or the pilot opening may be clogged with dust or debris.
Try gently blowing into the pilot opening to clear any blockage, then attempt to light it again. If that does not work, the igniter or thermocouple likely needs replacement — this is a job for a technician.
If you do not smell gas at all, the problem may be upstream: a closed gas valve, a tripped safety switch, or an issue with the gas line itself. Check that the main gas valve (usually a lever on the gas line entering the furnace) is in the "on" position — it should be parallel to the pipe, not perpendicular to it.
What to do if the pilot lights but the main burner does not
A pilot that stays lit but a main burner that will not ignite usually points to a faulty thermocouple. The thermocouple is a safety device that senses the pilot flame and tells the gas valve it is safe to send gas to the main burner. If the thermocouple is worn out or positioned incorrectly, the main burner will not receive gas even though the pilot is burning.
You can try repositioning the thermocouple slightly so the pilot flame touches it more directly, but if that does not work, the part needs to be replaced. This is not a repair most homeowners should attempt — a technician can replace it in 30 minutes to an hour.
Another less common cause is a blocked main burner port or a problem with the gas valve itself. Both of these also require professional diagnosis and repair.
Safety reminders when lighting a furnace
Never force any knobs or buttons. If something feels stuck or will not turn, stop and call a technician — forcing it can damage the valve or create a gas leak.
Do not use an electric lighter or anything that produces a spark near the furnace. Use a long-handled match or a lighter with a long flame so your hand stays safely away from the opening.
If you smell gas and cannot find the source, or if you smell gas after the furnace is running, turn off the furnace when ready, leave the house, and call your gas company's emergency line. Do not use your phone indoors — go outside to call.
If the pilot light goes out repeatedly even after you have lit it successfully, do not keep relighting it. This usually means the thermocouple is failing and needs to be replaced by a technician.
Frequently Asked Questions
How long should I hold the ignition button down?
Hold it for 30 to 60 seconds after the pilot flame catches. This gives the thermocouple time to heat up and signal the gas valve that the pilot is burning safely. If you release it too early, the pilot will go out.
What if I do not have a match or lighter?
You can use a long-handled grill lighter, a long taper candle, or even a piece of rolled paper lit from a stovetop — anything that produces a steady flame you can hold near the pilot opening without burning yourself. Avoid short lighters that force your hand too close to the opening.
Can I light the furnace if the thermostat is off?
Yes. The thermostat controls whether the main burner stays on, but the pilot light itself can be lit regardless of the thermostat setting. However, once you turn the knob to "On," the main burner will only ignite if the thermostat is calling for heat.
How often do I need to relight the pilot?
A healthy pilot light should stay lit all season without you relighting it. If you have to relight it more than once or twice a year, the thermocouple is probably wearing out and should be replaced before it fails completely.
What does the pilot flame look like when it is working correctly?
A healthy pilot flame is mostly blue with a small yellow or orange tip at the top. It should be about half an inch to one inch tall. If the flame is mostly yellow or orange, or if it is very small and flickering, the pilot opening may be dirty or the gas pressure may be low — have a technician check it.