Most of the no-heat calls our team runs on the first hard frost in Transylvania County come down to an older gas furnace with a pilot that blew out overnight. And in most homes, you can safely relight furnace pilot lights yourself: turn the gas control knob to Off, wait a full five minutes so raw gas can clear, turn the knob to Pilot, hold it down while you light the pilot flame, then keep holding until the thermocouple heats up and the flame stands on its own.
If you smell gas at any point, you stop, leave the house, and call your gas provider before you touch anything else. That is the whole procedure in one breath. The rest of this guide covers the details that keep it safe, and the handful of situations where relighting is the wrong move entirely.
Why Furnace Pilot Lights Go Out
A standing pilot usually goes out for one of four reasons: a draft, a worn thermocouple, a partially clogged pilot orifice, or a brief interruption in gas supply. A pilot light is a small standing flame that burns around the clock so it can ignite the main burners the moment the thermostat calls for heat.
No pilot, no ignition, no heat. Simple chain.
Drafts are the one we see most up here. A lot of the older cottages near downtown Brevard and the cabins out toward Lake Toxaway have the furnace sitting in a vented crawlspace, and a hard wind funneling through those foundation vents can snuff a weak pilot before dawn.
Newer builds in Connestee Falls tend to have sealed mechanical closets, so drafts are less of an issue there and thermocouple wear takes over as the usual suspect. Supply interruptions round out the list, and in this county those are usually propane problems, which deserve their own section because they change how the relight goes.
The Thermocouple Is the Part Doing the Deciding
The thermocouple is a small metal probe that sits in the pilot flame and generates a tiny electrical signal when hot, on the order of 25 millivolts on a good day. That signal holds a safety valve open. Per ANSI Z21.23 standards for thermocouples used in gas appliance systems, a reading below roughly 7 to 8 millivolts at the valve typically indicates a failing or misaligned probe.
When the probe wears out, corrodes, or drifts out of the flame, the signal drops, the valve closes, and the gas to the pilot shuts off. It’s a safety device doing exactly what it was designed to do, which is why a pilot that keeps dying is information, not just an annoyance.
The probe tip is usually darkened and slightly pitted by the time it fails, and the pitting starts on the side facing the flame. You can sometimes buy another season by repositioning a probe that has sagged out of the flame path, though the bracket that holds it tends to be rusted in place on anything that has spent years in a damp crawlspace, and the bracket screw strips before the bracket moves.
Propane Changes the Math Around Here
Downtown Brevard has natural gas lines, but a big share of Transylvania County heats on propane from a tank in the yard: Cedar Mountain, Lake Toxaway, most of the coves off Highway 276. This matters for pilot work because propane is heavier than air.
Natural gas rises and finds its way out of a leaky burner compartment. Propane sinks and pools in the lowest spot it can find, which in a crawlspace furnace installation means it pools right where you’re kneeling with a lighter.
The clearing wait exists for exactly this reason, and it’s more critical on propane than on natural gas, not less. Propane also runs at a different orifice pressure than natural gas, so a furnace converted between fuels without the right orifice kit produces a pilot flame that never looks right no matter how many times you relight it. We still find botched conversions in older cabins, usually where a previous owner did the swap.
How to Safely Relight Furnace Pilot Lights
The two steps that actually decide whether this goes well are the clearing wait and the thermocouple hold. Those two matter more than everything else in this article combined. We aren’t covering electronic ignition here, on purpose: if your furnace is a newer model, it likely doesn’t have a standing pilot at all, and forcing that system into this procedure causes more problems than it solves.
Read the lighting label on the furnace first. Every gas furnace has printed lighting instructions on the cabinet, and those override anything in a blog post, ours included. Turn the thermostat all the way down. You do not want the furnace calling for heat in the middle of this. Turn the gas control knob to Off. Fair warning from a crew that has done this a few hundred times: the knobs on older gas valves get stiff, the printed lettering wears off, and you’re usually reading tiny raised letters by flashlight while crouched in a crawlspace. Take your time. Set a timer and wait out the full clearing period. Not ninety seconds. Unburned gas needs time to disperse, and this wait is what makes the whole procedure safe. Turn the knob to Pilot and press it down. Holding it manually feeds gas to the pilot only. Some valves have a separate red button instead of a push-down knob; same function. Light the pilot with a long-reach lighter. A short match puts your knuckles somewhere they shouldn’t be. Keep the knob held down, then release slowly. Half a minute is the usual figure, though on a cold morning in an unheated crawlspace we tell people to hold somewhat longer, because a cold thermocouple takes longer to generate voltage. Let go too early and the flame dies. That fast. Turn the knob to On and restore the thermostat to your winter settings. The main burners should light on the next call for heat, and you should stay long enough to watch them do it, because how the burners catch tells you things the pilot can’t.
If the pilot dies when you release the knob, repeat the sequence once, holding closer to a full minute. But if it dies a second time, stop. Repeating it a fifth and sixth time (and yes, people do) just loads the burner compartment with frustration and gas.
Gas Clearing Wait Time: Why You Cannot Skip It
Nobody skips lighting the pilot. Nobody skips holding the knob, because the furnace won’t let them. The step people cheat is the wait, because standing in a cold crawlspace doing nothing feels pointless.
It isn’t. It’s the only step in the entire procedure that protects you from gas that already escaped. Count it out or set a phone timer, because everyone who guesses short.
When the Pilot Will Not Stay Lit
A pilot that lights fine but won’t stay lit is almost always a thermocouple problem, a flame quality problem, or a draft problem. The draft issue from the first section comes up here again, because a flame that gets pushed sideways stops bathing the thermocouple, and the safety valve reads that as flame failure even though the pilot is technically burning.
Before you condemn any parts, do the cheap check: on a windy day, stand at the furnace with the access panel off and watch whether the pilot flame dances. If it does, the fix might be blocking a foundation vent near the furnace or adding a draft shield, not replacing anything.
We solved a recurring pilot outage in a Pisgah Forest ranch house last winter with a piece of sheet metal bent into an L and screwed down next to the burner opening. Total parts cost was whatever scrap was on the truck.
Reading the Pilot Flame
The flame itself tells you most of what you know:
| What the pilot flame looks like | What it usually means |
|---|---|
| Steady blue cone wrapping the thermocouple tip | Healthy pilot |
| Yellow, lazy, flickering | Dirty pilot orifice or combustion air problem |
| Small blue flame that barely reaches the probe | Partially clogged orifice or low gas pressure |
| Flame leaning hard to one side | Draft hitting the burner compartment |
The key detail: the thermocouple has to be in the flame, not near it. A quarter inch of misalignment is enough to shut the valve. The top third of the probe should sit inside the blue cone, and on most pilot assemblies there’s a bracket hole that positions it correctly, assuming nobody has bent the assembly reaching past it with a shop vac.
Thermocouple vs. Flame Sensor: Different Parts, Crossed-Up Advice
Now, a confession on the repair side. We go back and forth on whether homeowners should clean a pilot orifice themselves, and honestly our own techs do not fully agree with each other on it. Compressed air on a visibly sooty pilot assembly is probably fine.
Poking anything into the orifice is where we get nervous, because we have seen a wire brush bristle turn a partial clog into an enlarged opening and a lazy, oversized flame. And one more correction while we are being honest: people use thermocouple and flame sensor interchangeably, and they aren’t the same part. The flame sensor on a modern electronic-ignition furnace works on a completely different principle, flame rectification instead of millivolt generation, so advice for one gets misapplied to the other constantly, including by people who should know better. The ugly part is that a thermocouple can also behave fine when tested cold and still drop out once everything heats up and expands, which is why some of these come back a week later.
Should You Replace the Thermocouple Yourself?
Plenty of contractors will tell you no homeowner should ever touch a gas valve connection. We think that’s overcautious on a standard thermocouple swap.
The part costs about a typical figure at the hardware store in Brevard, it threads into the valve with a small brass nut, and the connection carries millivolts, not line-pressure gas. A reasonably handy person with an adjustable wrench can do it.
The mistake that ruins the job is overtightening. That brass fitting seats a soft copper tip against a contact inside the valve, and it wants finger tight plus about a quarter turn with the wrench.
Crank it down like a plumbing fitting and you deform the tip, and now the brand new part reads worse than the old one. The second mistake is kinking the copper lead while routing it, which breaks the conductor inside even when the outside looks fine.
Recurring Pilot Outage: Venting and Backdraft Causes
A 1989 Goodman off Reasonover Road, last November. The homeowner had relit the pilot eleven times over two weeks before calling us, and by then he could do the whole sequence blindfolded. New thermocouple, correctly installed, and he had done it himself. Good flame, good alignment. The pilot still died, always overnight.
The actual cause was a flue problem. A section of vent pipe in the attic had separated at a joint, and on cold, still nights the flue would backdraft, pushing a slug of cold outside air down through the furnace and out across the burner compartment. The pilot never stood a chance, and no amount of thermocouple work was going to fix it. That job is why we tell people a pilot that only dies in certain weather is a venting clue, and it’s also why relighting eleven times without asking why is the wrong instinct.
A backdrafting flue is a carbon monoxide pathway, not just a pilot nuisance.
Standing Pilot Light Energy Cost: BTU and Fuel Consumption
That little flame isn’t free. A typical standing pilot consumes approximately 900 to 1,000 BTUs per hour, according to DOE research that underpinned the federal push toward electronic ignition in residential furnaces, adding up to roughly 600,000 to 700,000 BTUs a month of continuous burn. We metered one on a service call in Rosman and it penciled out to just under five gallons of propane a month, which at current local propane prices is real money over a heating season, and pure waste in July.
This is a big part of why federal efficiency standards pushed manufacturers to electronic ignition decades ago, and why almost nothing sold today has a standing pilot. If yours does, the furnace is old enough that the pilot is one line item on a longer list of signs your HVAC system is failing. Shutting the pilot off for the summer is legitimate and the lighting label tells you how; you just relight it in fall using the same procedure above.
After a Propane Runout, Relighting Is a Different Job
The propane point from earlier circles back here. When a tank runs dry, two things happen. First, air gets into the gas lines, so your first several relight attempts feed the pilot a mix that won’t burn, and people wrongly conclude the furnace broke while the tank was empty. You may have to hold the knob through three or four full attempts just to purge the line. Second, and this is the part almost nobody knows, a runout is legally an interruption of service, and the propane supplier is supposed to perform a leak check on the system before restoring gas.
If your delivery driver relights appliances after a runout, that’s why. If you refill and relight yourself without any pressure check, you’re skipping the step that catches a fitting that started weeping while the system sat empty and depressurized. The CPSC warns that home heating equipment left improperly checked after service interruptions is one of the leading sources of residential CO incidents.
When Not to Relight a Furnace Pilot Light
Do not relight if you smell gas before opening the panel, that is the situation where you leave and call from outside. Our lead HVAC technician, Chris Trantham, who has diagnosed gas appliance systems in Transylvania County for over 20 years, puts it plainly: “If you can smell gas before you have even opened the panel, you do not light anything. You leave, and you make the call from outside.”
Beyond that, do not keep relighting a pilot that has gone out three times in a week, a pilot in a furnace with scorch marks or soot streaking around the burner compartment, or a furnace that rumbles or booms when the main burners catch. Delayed ignition and a compromised heat exchanger aren’t homeowner projects.
These are also situations where checking your carbon monoxide detectors before winter becomes especially critical. Honestly, a stubborn pilot on a furnace past twenty years old is usually the equipment telling you something bigger, and we would rather have that conversation early than after a February cold snap.
When It Is Time to Call Us Instead
Our team at MAC Heating & Air Conditioning, Inc. has been relighting and repairing these systems around Brevard, NC since 1990, from Rosman to Pisgah Forest and everywhere between.
If the procedure above gets your heat back, good, that’s exactly what this guide is for. But if your pilot keeps dying and you’re done crawling under the house, call us and schedule a furnace repair diagnostic visit: we come to you, find the actual cause, and hand you a written report.
Frequently Asked Questions
How long do you hold the pilot button down when relighting a furnace?
Hold the pilot button or knob down for at least 30 seconds after the flame lights, and longer (closer to 60 seconds) if the furnace is sitting in a cold, unheated space such as a crawlspace. The thermocouple, a small metal probe that sits in the pilot flame, needs time to heat up and generate enough voltage to hold the gas safety valve open on its own. Releasing the knob before the thermocouple reaches operating temperature cuts the gas supply and kills the flame immediately.
Why does my furnace pilot light keep going out after relighting?
A pilot that relights but dies again within hours or days almost always points to a failing thermocouple rather than a draft or gas supply issue. The thermocouple generates roughly 25 millivolts when healthy; as the probe corrodes or drifts out of the flame path, that signal weakens until the safety valve can no longer stay open. If the pilot dies the moment you release the knob on two consecutive attempts, stop relighting and have the thermocouple inspected or replaced.
Is it safe to relight a furnace pilot light yourself on propane?
Yes, but the five-minute clearing wait before you introduce any ignition source is more critical on propane than on natural gas. Propane is heavier than air, so unburned gas sinks and pools at floor level rather than dispersing upward. In a crawlspace installation, that means gas can accumulate right at ground level where you are positioned with a lighter. Allow the full five minutes with the gas control knob turned to Off, and leave immediately without lighting anything if you smell gas at any point.
What causes a furnace pilot light to go out overnight?
The four most common causes are a draft reaching the burner compartment, a worn or misaligned thermocouple, a partially clogged pilot orifice, and a brief interruption in gas or propane supply. Furnaces installed in vented crawlspaces are especially vulnerable to drafts because wind can funnel through foundation vents and extinguish a weak flame before morning. A pilot that goes out repeatedly under calm conditions with no supply issues almost always indicates thermocouple wear rather than a draft problem.