Furnace Pilot Light Keeps Going Out?
If you are relighting the pilot every few days, the furnace is telling you something. Usually it's a twelve-dollar part. Occasionally it's a reason to stop relighting and call.
Quick Answer
A pilot that lights but won't stay lit after you release the knob is almost always a worn thermocouple, the small copper probe that sits in the pilot flame and tells the gas valve it is safe to keep the gas on. When it weakens, the valve shuts the pilot off as a safety measure. The other common causes, in order: a dirty pilot tube giving a weak, yellow, wavering flame, a draft blowing the flame off the thermocouple, and a failing gas valve. These furnaces are older by definition, so the fix comes with an honest read on how much life the furnace has left.
Stop and call from outside if you smell gas at any point, if the pilot goes out with a pop or a whoosh, or if the main burners light with a delay and a boom. Those are not thermocouple problems.
The 4 Causes, Most to Least Likely
1. Worn thermocouple (the usual suspect)
The tell: the pilot lights fine while you hold the knob down, then dies the moment you let go, or within a minute. The thermocouple generates a tiny voltage from the flame's heat; after years in the fire it can't make enough to hold the valve open. It is an inexpensive part and a quick replacement, and a good tech will also check that the new one sits properly in the flame, because a misaligned thermocouple fails the same way a worn one does.
2. Dirty or partly blocked pilot tube
Dust, rust flakes, and spider webs narrow the pilot orifice until the flame is small, yellow, and lazy instead of a crisp blue cone. A weak flame doesn't heat the thermocouple enough, so the valve drops out. The flame color is the clue: a healthy pilot is mostly blue and steady. A yellow, wavering pilot needs cleaning, and the same rule applies to the main burners, which is why we have a whole page on a yellow furnace flame.
3. A draft at the burner compartment
A pilot that goes out on windy nights, or when the blower kicks on, is being blown off the thermocouple. Causes include a missing or loose burner door, a cracked or rusted heat exchanger letting blower air into the combustion area, or a flue problem. A missing door is a two-minute fix. The other two are a tech's call, and a heat exchanger crack is a carbon monoxide risk that ends the relighting for good.
4. Gas valve or gas supply
If the thermocouple is new, the pilot is clean and blue, and it still won't hold, the valve's pilot solenoid may be failing, or gas pressure may be low or intermittent. Low pressure can also show up as a pilot that dims when other gas appliances run. On a furnace old enough to have a standing pilot, a failed gas valve is often the point where replacement makes more sense than repair, and we will show you the numbers both ways.
What's Safe to Do Yourself
Relight it once, by the label
Every furnace with a standing pilot has relighting instructions printed on the unit. Turn the gas control to OFF, wait five full minutes for any gas to clear, then follow the label: PILOT, hold, light, keep holding 30 to 60 seconds, release. If you smell gas during the five-minute wait, stop, leave the house, and call the gas company and us from outside.
Watch the flame for a minute
Blue and steady, wrapping the thermocouple tip: good. Yellow, small, or dancing: the tube needs cleaning or a draft is hitting it. Goes out the moment you release the knob: thermocouple. What you see tells us what part rides on the truck.
Check the burner door and anything blowing on it
Make sure the burner compartment door is on and seated. Note whether the pilot dies when the blower starts, when the wind picks up, or when the dryer or water heater runs. Those patterns point at a draft or at gas pressure, and they are worth saying when you call.
Stop relighting after the second time
One relight is troubleshooting. Relighting every night is running a furnace that keeps trying to shut itself off for a reason. Leave the gas control on OFF and call; the fix is cheap and the risk of ignoring a draft or a cracked exchanger is not.
Related pages
Pilot or burners burning yellow: yellow flame on your gas furnace. Newer furnace with no pilot that won't light: furnace blowing cold air and the blinking-light code checker. A burning or gas smell: furnace smells like burning. No heat from anything: the no-heat checklist.
Ready for a pro to take it from here?
Thermocouples and pilot assemblies ride on our winter trucks, and every standing-pilot call gets an honest read on the furnace's remaining life, in writing. Our heating repair crews run same-day calls across Central Arkansas — including heating repair in Bryant, heating repair in Benton, heating repair in Little Rock, North Little Rock, Conway, Sherwood and Maumelle. Night, weekend, or holiday? 24 hour heating repair is a real person on the line, not a recording.
Relit It Twice? Leave It Off and Call.
$149 flat diagnostic, $75 credited to the repair, and same-day heating repair across Little Rock, Bryant, Benton, Conway, and Central Arkansas.
Call 501-307-5959