To relight a furnace pilot light safely, turn the gas valve to Off, wait five minutes for residual gas to clear, set the thermostat to its lowest setting, then hold a long lighter to the pilot orifice while pressing the reset button for 30 to 60 seconds until the flame holds. If the pilot won't stay lit after two attempts, stop and call a licensed technician - a thermocouple, dirty orifice, or draft problem is usually the cause. This guide walks you through the full procedure, the safety checks that matter, and the reasons a pilot light keeps dying in the first place.
Most Idaho homes with standing-pilot furnaces are running equipment installed between the late 1980s and the mid-2000s. That age range matters: the pilot assembly on a 20-year-old furnace is often the first component to fail, and it fails in ways that look identical to a simple draft blowing out the flame. Knowing the difference saves you a cold night.
What a Furnace Pilot Light Actually Does
A furnace pilot light is a small, continuously burning flame that ignites the main gas burner when your thermostat calls for heat. It also heats a thermocouple or thermopile - a pair of dissimilar-metal sensors that generate a tiny electrical current. That current tells the gas valve it's safe to open. No flame, no current, no gas. The system is designed to fail closed.
On older standing-pilot furnaces, the pilot burns 24/7, 365 days a year. On newer intermittent-pilot or hot-surface-ignition models, there is no standing flame at all - the furnace sparks or glows to light the burner only when heat is needed. If you don't see a pilot flame on your furnace, check the model plate first. You may be looking for a pilot that was never there.
Standing-pilot furnaces are still common across Idaho, particularly in older homes and rural properties where the equipment was installed before high-efficiency condensing units became standard. If your furnace has a round dial gas valve with Off, Pilot, and On positions, you have a standing pilot.
Safety First: Before You Touch Anything
Furnace pilot light safety comes down to three rules: no gas smell, no open flame near the valve, and no repeated attempts if the pilot won't hold.
If you smell gas - a rotten-egg or sulfur odor - stop immediately. Do not flip a light switch, do not use your phone near the furnace, and do not try to relight anything. Leave the house, call your gas utility's emergency line from outside, and wait for the all-clear. Gas odor is the one scenario where DIY ends.
If there's no gas smell, you're clear to proceed. Gather what you need:
- A long-barrel utility lighter or a long match (never a short match - you'll burn your knuckles)
- A flashlight
- A clean rag or soft brush for dust around the burner compartment
- Your furnace's model and serial number (photograph the plate before you start)
Turn the thermostat to its lowest setting or Off. You don't want the main burner firing while you're working on the pilot assembly. Give the furnace 10 minutes to cool if it was recently running.
One more thing: know where your gas shutoff valve is before you start. It's usually a quarter-turn ball valve on the gas line within a few feet of the furnace. If anything goes wrong, that's your first move.
Step-by-Step: How to Relight a Furnace Pilot Light
The exact procedure varies slightly by brand - Carrier, Trane, Lennox, and Rheem all use slightly different gas valve designs - but the sequence is consistent. Here's the step-by-step relight furnace pilot light process we use in the field.
- Set the gas valve to Off. The dial or knob on the gas valve has three positions. Turn it to Off and wait a full five minutes. This clears any residual gas that accumulated while the pilot was out.
- Set the thermostat to its lowest setting. This prevents the main burner from firing during the relight.
- Locate the pilot orifice and thermocouple. Remove the burner access panel. The pilot assembly is a small metal bracket near the main burner, with a thin tube running to it and a thicker probe (the thermocouple) sitting in the flame path.
- Clean around the orifice. Dust, rust flakes, and spider webs are common culprits. A soft brush or a blast of compressed air clears most of it. Don't poke a wire into the orifice - you'll deform it.
- Turn the gas valve to Pilot. Push the knob down and hold it. This feeds a small amount of gas to the pilot orifice only.
- Light the pilot. Hold your long lighter or match to the pilot orifice while continuing to press the knob. The flame should light within 2 to 3 seconds.
- Hold for 30 to 60 seconds. Keep pressing the knob for a full minute. This lets the thermocouple heat up and generate enough current to hold the gas valve open on its own.
- Release the knob slowly. If the pilot stays lit, turn the gas valve to On. If it goes out, repeat steps 1 through 7 once. If it still won't hold, stop.
- Restore the thermostat. Set it back to your normal temperature and replace the access panel. The main burner should fire within a minute or two.
If the pilot lights but the main burner never comes on, the problem is upstream of the pilot - a thermostat, a limit switch, or a control board. That's a diagnostic job, not a relight job.
Why Does My Furnace Pilot Light Keep Going Out?
A furnace pilot light that keeps going out is almost always one of five things: a failing thermocouple, a dirty pilot orifice, a bad gas valve, a draft pulling the flame away from the thermocouple, or a flame sensor that's reading incorrectly. Here's how to tell them apart.
Thermocouple failure
The thermocouple is the most common failure point on a standing-pilot furnace. It's a $10 to $25 part, and it degrades with age - typically after 8 to 12 years. When it fails, the pilot lights but won't stay lit once you release the knob. That's the classic signature.
Dirty pilot orifice
A partially blocked orifice produces a weak, yellow, or flickering flame instead of a steady blue one. The flame doesn't reach the thermocouple properly, so the thermocouple never gets hot enough. Cleaning the orifice usually fixes it. In Idaho, dust and dry air make this more common than in humid climates.
Draft or backdraft
If the pilot lights fine on a calm day but blows out on windy ones, you have a draft problem. Check the flue, the combustion air intake, and any recent changes to the room - a new exhaust fan, a closed door, or a return-air register can all change pressure enough to pull the flame off the thermocouple.
Bad gas valve
If the pilot lights and holds but the main burner never fires, the gas valve or its internal solenoid is the likely culprit. This is not a DIY repair. Gas valve replacement requires shutting off the gas supply, testing for leaks, and verifying manifold pressure - all of which need a licensed technician and a manometer.
High-limit or rollout switch tripping
Some furnaces shut down the pilot circuit when a safety switch trips. A tripped high-limit switch usually means restricted airflow - a clogged filter, a blocked return, or a dirty blower wheel. A tripped rollout switch means flame escaped the heat exchanger, which is a serious safety issue. If you reset it and it trips again, stop using the furnace and call for service.
If your pilot light won't stay lit after relighting, don't keep cycling it. Each failed attempt pushes unburned gas into the combustion chamber. Two attempts is the limit.
What to Watch Out For
Most pilot-light injuries and furnace damage we see come from a short list of avoidable mistakes.
- Using a short match or a cigarette lighter. Your hand ends up directly over the pilot orifice. Use a long-barrel lighter.
- Skipping the five-minute wait. Residual gas needs time to clear. Five minutes is the minimum, not a suggestion.
- Pressing the reset button repeatedly. If the pilot won't hold after two tries, the problem is mechanical or electrical, not procedural.
- Poking the orifice with a wire or paperclip. The orifice is a precision-machined hole. A wire scratch changes the flame shape permanently.
- Ignoring a yellow or orange pilot flame. A healthy pilot flame is blue with a slight yellow tip. A fully yellow flame means incomplete combustion - a carbon monoxide risk.
- Relighting a furnace that's been flooded or recently serviced. If the gas line was opened, call a technician to pressure-test before you light anything.
One more: if your carbon monoxide detector has ever gone off in the house, do not relight the furnace until a technician has inspected the heat exchanger and combustion air path. CO alarms are not false alarms until proven otherwise.
When to Call a Professional
Call a professional if the pilot won't stay lit after two attempts, if you smell gas at any point, if the flame is yellow instead of blue, if the main burner never fires, or if your CO detector has triggered. Those five conditions cover roughly 90% of the pilot-light calls we run.
At Furnace Pros Idaho, we diagnose pilot and ignition problems with a manometer, a multimeter, and a combustion analyzer - the same tools we use on every Furnace Repair in Idaho call. We test thermocouple output in millivolts, verify manifold pressure against the data plate, and check the heat exchanger for cracks before we call a furnace safe to run.
If your furnace is 15 years or older and the pilot assembly has failed once, it will fail again. At that point, a Furnace Tune-Up in Idaho that includes a full pilot assembly inspection is cheaper than a mid-winter emergency call. We also see a lot of this in older homes around Furnace Repair in Boise, where the housing stock skews older and standing-pilot furnaces are still common.
We don't guess. We test, we replace what's failed, and we run the furnace through a full heat cycle before we leave.
Frequently Asked Questions
How do I relight my furnace pilot light safely?
Turn the gas valve to Off and wait five minutes. Set the thermostat to its lowest setting. Turn the valve to Pilot, press and hold the knob, and hold a long lighter to the pilot orifice. Keep holding for 30 to 60 seconds after the flame lights, then release and turn the valve to On.
Why does my furnace pilot light keep going out?
The most common cause is a worn thermocouple - a $10 to $25 part that typically fails after 8 to 12 years. Other causes include a dirty pilot orifice, a draft pulling the flame off the thermocouple, a failing gas valve, or a tripped safety switch. A technician can isolate which one in under 30 minutes.
Is it safe to relight a furnace pilot light yourself?
Yes, if there is no gas odor, you use a long lighter, and you wait the full five minutes before lighting. It is not safe if you smell gas, if the pilot won't hold after two attempts, or if your CO detector has triggered. Those three situations require a licensed technician.
What should I do if my furnace pilot light won't stay lit?
Stop after two attempts. Each failed relight pushes unburned gas into the combustion chamber. The likely cause is a failed thermocouple, a dirty orifice, or a gas valve issue - all of which need a technician with a multimeter and manometer to diagnose correctly. Call for service rather than cycling the pilot again.
Can I relight a furnace pilot light without a professional?
For a simple draft blowout on a standing-pilot furnace, yes - the procedure takes about five minutes and needs only a long lighter. For anything involving a gas smell, a yellow flame, a pilot that won't hold, or a furnace over 15 years old, call a professional. The diagnostic tools alone cost more than a service call.
Get Help with Furnace Repair in Idaho
If your pilot light won't stay lit, your main burner won't fire, or you'd rather not troubleshoot a gas appliance on a cold Idaho night, our team handles it. We diagnose the pilot circuit, test the thermocouple, verify gas pressure, and confirm the furnace runs a full heat cycle before we leave.
Call Furnace Pros Idaho at (833) 588-3865. We'll get your heat back on.