Why Does My Pilot Light Keep Going Out? (5 Causes & Fixes)
Pilot light keeps going out? Start with the thermocouple. Most cases cost $7-15 to fix yourself. Here are the 5 causes and what to do about each.
Quick answer: A dirty or failing thermocouple causes most pilot light problems. When the pilot goes out the moment you release the ignition button, clean the thermocouple tip with 600-grit emery cloth first. If it still dies after cleaning, replace the thermocouple, a $7-15 part that installs in about 20 minutes. Drafts, a clogged pilot orifice, and low gas pressure are the other causes to rule out in that order.
Your furnace fired up fine all last winter. Now it’s the first cold morning of the season, you go to light it, and the pilot keeps dying the moment you release the button. Or maybe it stays lit for a few hours and then goes out overnight.
Both patterns point to the same short list of suspects. Work through them in order and most pilot light problems get resolved without a service call.
This applies equally to furnaces and water heaters. The pilot assembly and thermocouple work the same way on both. If you’re also noticing unusual water heater noises alongside pilot problems, you may have more than one issue developing.
1. Dirty Thermocouple
This is the fix that handles most pilot light problems, and most homeowners have never heard of it.
The thermocouple is a thin metal probe, roughly the size of a pencil, that sits with its tip directly in the pilot flame. It generates a small electrical current when heated, and that current is what tells the gas valve to stay open. When the tip gets coated with soot, oxidation, or mineral deposits, it can’t generate enough current, and the valve closes.
The fix is simpler than it sounds. Shut off the gas, let everything cool for 20 minutes, then find the thermocouple. It’s the probe closest to the pilot, usually a copper-colored rod with a wire running from its base down to the gas valve. Gently rub the tip with 600-grit emery cloth, just enough to clean the metal surface without removing material. Reconnect it, relight the pilot, and hold the ignition button for 45-60 seconds to let the thermocouple heat up fully before releasing.
About half the time, that takes care of it.
2. Failing Thermocouple
If you cleaned the thermocouple and the pilot still dies the moment you release the button, the thermocouple has weakened. Even clean metal generates less current as it ages, and after 7-10 years of daily cycling, many thermocouples simply can’t hold the gas valve open anymore.
Replacement thermocouples run $7-15 at any hardware store. They’re not model-specific in most cases. A universal thermocouple that matches the thread size and length works on most residential furnaces and water heaters. Fluidmaster and Honeywell both make reliable universal thermocouples. The 30-inch length fits most residential appliances, but measure the existing one first if you want to be certain.
The installation takes about 20 minutes: unscrew the old one at both ends (the pilot bracket and the gas valve connection), thread in the new one finger-tight, and test.
This repair handles the majority of repeat pilot light failures. If you’ve relit the pilot three times in the past month, the thermocouple is almost certainly the problem.
3. Clogged Pilot Orifice
The pilot orifice is a small hole that meters the gas flowing to the pilot flame. Dust, lint, and rust particles can partially obstruct it over time. When that happens, the pilot flame becomes small and irregular instead of crisp and blue at the base with an orange tip. A weak flame doesn’t heat the thermocouple enough to hold the gas valve open.
You can usually see this problem without tools. When the pilot is lit, look at the flame color and shape. A clean pilot flame is mostly blue with a yellow-orange outer tip, steady, and sized to cover the thermocouple tip completely. A clogged orifice produces a yellow, wavering flame, or a flame that only burns on one side.
To clean it: shut off the gas and let everything cool. Use a soft-bristle brush around the orifice opening to clear loose debris. Do not insert a wire or needle into the orifice. The hole has a precise size, and enlarging it will make things worse. Compressed air aimed at the opening from a distance clears most blockages without that risk.
4. Drafts Near the Appliance
A pilot flame burns with less fuel than a candle, which makes it vulnerable to air movement. Basements and utility rooms with gaps around utility penetrations, poorly fitted doors, or uninsulated windows can create enough draft to extinguish the pilot.
The test: while the pilot is lit, hold your palm six inches from the appliance and move it slowly around the base. If you feel airflow, trace it to the source. Common culprits are utility room doors that don’t seal fully, gaps around dryer venting, and open windows on a windy day.
If a draft is blowing out the pilot repeatedly, foam weather seal tape around the utility room door is a $5 fix that often solves it. For gaps around penetrations, low-expansion foam sealant handles it.
5. Low Gas Pressure or a Faulty Gas Valve
If the thermocouple tests good, the orifice is clear, and there’s no draft, the remaining suspects are low gas pressure or a failing gas control valve.
Low gas pressure means the appliance isn’t getting enough gas to sustain the pilot. This can happen if the gas meter is partially closed, if other high-demand appliances are running simultaneously, or in rare cases if there’s a supply pressure issue from the utility. Check that the gas shutoff valve near the appliance is fully open. It should be parallel to the pipe, not at an angle.
A faulty gas control valve is less common but does fail, especially on water heaters more than 10 years old. The valve controls gas flow to both the pilot and the main burner. If its internal thermocouple seat is worn, it won’t hold open even with a good thermocouple. This is not a DIY repair.
Common Mistakes
Releasing the button too soon. The 45-second hold gives the thermocouple time to reach operating temperature. Many people hold for 10-15 seconds, the pilot looks stable, they let go, and it dies. Hold the full 45 seconds, especially on a cold appliance.
Poking the pilot orifice with a wire. This is the most common self-inflicted problem. The orifice is sized precisely, and even a small wire can enlarge it enough to change the flame pattern. Use compressed air only.
Skipping the thermocouple cleaning step. Most pilot problems get diagnosed as a faulty thermocouple when cleaning would have done it. A $7 part is not expensive, but neither is emery cloth, and knowing the thermocouple is genuinely failed versus dirty is worth five extra minutes.
Relighting without letting gas clear. If you smell gas when you approach the appliance, leave the area and call your gas utility’s emergency line. That is a different problem from a pilot that keeps going out.
If your furnace has other symptoms alongside the pilot problem (won’t stay on, runs but doesn’t heat), furnace not turning on troubleshooting covers the broader diagnostic.
When to Call a Pro
If you smell gas at any point during this process, stop and call your gas utility’s emergency line. If you’re not sure whether what you’re smelling is gas, the rotten egg smell guide walks through identifying the source.
For a failed gas valve: testing and replacing a gas control valve involves working directly with gas supply lines and requires pressure testing equipment. The National Fuel Gas Code (NFPA 54) requires that any work on gas piping beyond the appliance shutoff be performed by a licensed professional in most US jurisdictions. The thermocouple and pilot orifice work described here stays upstream of that line and is routine homeowner maintenance.
For appliances older than 15 years with repeated pilot issues: a technician can assess whether repair or replacement makes economic sense. A new 40-gallon water heater runs $400-700 installed; for an appliance in its last years, that math often works out in favor of replacement over a string of repairs.
Before the next heating season, the annual furnace prep checklist covers the full set of maintenance tasks, including thermocouple cleaning.
FAQ
Why does my pilot light go out when I release the button? Almost always a thermocouple issue. The thermocouple needs 30-45 seconds of heat to generate enough current to hold the gas valve open. If the pilot dies immediately on release, clean the thermocouple tip first with 600-grit emery cloth. If it still fails after cleaning, replace it. It’s a $7-15 part at any hardware store.
How long should I hold the pilot button down? At least 45 seconds on a cold appliance, 30 seconds if it’s already warm. The thermocouple heats up gradually and needs time to reach operating temperature before you release. Rushing this step is the single most common reason a relight attempt fails.
Can I replace a thermocouple myself? On most furnaces and water heaters, yes. Universal replacement thermocouples are available at any hardware store for $7-15. The process takes about 20 minutes: unscrew the old one at the pilot bracket and gas valve, thread in the new one finger-tight, and test. Shut off the gas first and confirm no gas odor before relighting.
Why does my pilot light keep going out in winter? Cold weather itself isn’t the cause, but winter brings two related problems: increased draft through utility room doors from cold air infiltration, and higher demand on the gas supply when multiple appliances run simultaneously. Check for drafts near the appliance and make sure the gas shutoff is fully open.
What color should a pilot flame be? A healthy pilot flame is mostly blue at the base with a yellow-orange outer tip. It should be steady and large enough to cover the thermocouple tip completely. A yellow, flickering, or small flame usually means a dirty orifice, low gas pressure, or a draft problem.
Is it dangerous if my pilot light keeps going out? If the pilot fails, the gas valve closes. The appliance won’t get gas, so there’s no gas leak from the appliance itself. The danger comes if you smell gas, which means gas is flowing without combustion. That’s not normal pilot behavior and needs immediate attention. A pilot that simply won’t stay lit, with no gas smell, is a maintenance issue.
How often should a thermocouple be replaced? Most thermocouples last 7-10 years under normal use. If your water heater or furnace is 8-plus years old and experiencing pilot problems for the first time, the thermocouple is a reasonable first part to replace even without confirming it’s failed. At $7-15, it’s worth eliminating it as a variable.
Can a dirty air filter cause pilot light problems? Not directly. A clogged filter restricts airflow through the furnace and affects main burner efficiency, but it doesn’t reach the pilot assembly. If you’re chasing a furnace problem and haven’t changed the filter in more than 90 days, do that first. It’s not the pilot issue, but it may be contributing to other problems.
Conclusion
The thermocouple handles most pilot light problems. Clean it first, replace it if cleaning doesn’t hold. Rule out the orifice and drafts next. If none of those fix it, low gas pressure or a failing gas valve is a job for a technician.
For the full range of heating and cooling problems, the HVAC troubleshooting guide covers everything from air conditioning failures to furnace diagnostics in one place.