A gas fireplace pilot that won’t stay lit usually points to a weak thermocouple or thermopile, a dirty pilot, low gas flow, or a tripped safety device.
When a pilot keeps going out, the room gets cold and nerves fray. The good news: most causes are routine and fixable with basic checks. This guide lays out clear steps that respect safety rules and keep your hearth heat-ready.
Quick Safety And Setup Checks
Smell gas? Stop here, turn the control to OFF, and leave the area. Call your gas supplier or a licensed technician from outside the home. Carbon monoxide alarms should be working on every level of a home that uses fuel-burning appliances; see the NFPA carbon monoxide safety tips for placement and testing. Crack a window while you troubleshoot, and keep kids and pets clear of the hearth.
Gas Fireplace Pilot Keeps Going Out: Causes And Quick Checks
Match the symptom with the likely source and a fast first check.
| Symptom | Likely Cause | Fast Check |
|---|---|---|
| Pilot lights, then dies in 5–60 seconds | Thermocouple weak; flame too small; flame not hitting sensor | Hold the knob in “Pilot” a full minute; confirm a sharp blue flame wraps the sensor tip |
| Pilot stays lit but drops when main burner starts | Thermopile output low; loose switch loop; high resistance | Wiggle switch wires; try a direct jumper at the valve to bypass the wall switch |
| Yellow, lazy, or lifting pilot | Dust or spider webs; blocked pilot orifice; wrong air mix | Turn gas off; blow out the pilot hood and air slots with canned air |
| No pilot at all | Air in line; closed shutoff; empty LP tank; no spark | Verify the manual shutoff is parallel to the pipe; follow the lighting label step by step |
| Pilot drops only on windy days | Downdraft or weak vent draw | Crack a nearby window; check cap and terminations for nests or debris |
| Vent-free set shuts off after minutes | Oxygen depletion sensor (ODS) doing its job | Clean ODS air slots with canned air; provide more fresh air for the room |
How The Pilot, Thermocouple, And Thermopile Work
The pilot flame is more than a tiny light. It heats a sensor that makes millivolts of electricity. A thermocouple (on standing-pilot systems) produces a few dozen millivolts that hold the pilot valve open only while the flame is heating it. A thermopile (common on many electronic ignition models) makes a few hundred millivolts to power the main gas valve and the switch loop. If the flame is weak or not aimed at the sensor, the safety circuit drops gas and the pilot goes out.
Manufacturers specify where the flame should land on the sensor. Hearth & Home Technologies notes the pilot flame should touch the thermocouple tip for reliable operation; see the pilot flame guidance in their owner manuals, such as the Natural Blaze series note that “the pilot flame should just touch the top of the thermocouple tip.” Reference: Hearth & Home manual excerpt.
Step-By-Step: Fix A Pilot That Won’t Stay Lit
1) Relight By The Book
Follow the lighting label or your owner’s manual. Give the pilot button a full 30–60 seconds of hold time so the safety magnet warms and latches. If your model has a glass front, remove and reinstall it only as the manual describes.
2) Confirm Fuel And Shutoffs
The appliance shutoff should be fully open. Natural gas homes rely on supply pressure set by the utility regulator; propane systems need a filled tank and a two-stage regulator sized for the load. If the fireplace sat idle all summer, a little air in the line may require several lighting attempts.
3) Clean The Pilot Assembly
Turn the gas off. Use canned air to clear dust from the pilot hood, air inlets, and the small orifice. Avoid poking metal into the orifice; that can damage precision parts. On vent-free sets, keep the ODS intake slot clean; it meters air to sense low oxygen.
4) Aim For The Right Flame
Relight and watch the pilot. You want a tight blue flame that kisses the upper third of the thermocouple or fully bathes the thermopile. Many valves include a small pilot adjustment screw; a quarter-turn can make a big difference. Only adjust if your manual shows this control and the model allows it. If your flame can’t be shaped, the orifice may be dirty or mis-sized for the fuel.
5) Reseat The Thermocouple
On standing-pilot units, snug the thermocouple nut at the gas valve finger-tight plus a slight turn with a wrench. Don’t overtighten. Make sure the tip sits squarely in the flame where the flame is blue, not yellow.
6) Check Millivolts If You Own A Meter
A healthy thermocouple often reads around 25–35 mV with the flame on. A healthy thermopile typically shows several hundred mV with no load and less under load. Low readings point to a tired sensor, poor flame contact, or high resistance in the switch loop. Replace only after the flame is strong and aimed correctly.
7) Inspect The Switch Loop
Wall switches, toggles, remotes, and safety switches add resistance. Bypass the wall switch briefly by touching the two valve terminals together with a short jumper to see if the burner holds. Replace weak batteries in any remote receiver or ignition module. Re-crimp any loose spade connectors at the valve.
8) Watch For Safety Trips
Spill switches and high-limit switches open the circuit when venting is poor or temperatures spike. Reset only after fixing the cause. If a spill switch trips again, stop and schedule service.
9) Fix Draft Problems
Wind across a termination cap can pull the pilot off the sensor. Clear leaves or nests from the cap, see that intake and exhaust paths are open on direct-vent models, and verify the cap is seated correctly. On chimney-vented units, a cold flue or tight house can cause downdraft; crack a nearby window and try again.
10) Know When To Call A Pro
Persistent dropouts, soot on glass, repeated spill-switch trips, glass that won’t seal, or any signs of gas leakage call for service. A tech can verify inlet and outlet pressures, read loaded millivolts at the valve, and replace parts safely.
Vent-Free Notes: Oxygen Depletion Sensor (ODS)
Vent-free log sets and heaters use an ODS pilot. If room oxygen falls, the flame lifts away from the sensor and the unit shuts down. Dust can block the tiny air slots near the pilot, so gentle cleaning with canned air often restores steady operation. Do not swap or drill an ODS pilot; the orifice is tuned to the fuel type and tampering ruins the safety function.
Draft, Makeup Air, And Chimneys
Tight homes or big exhaust fans can pull air down a flue. That downdraft chills the pilot or lifts it off the sensor. A quick test is to crack a nearby window and try again. Check the chimney cap and screen for debris. On direct-vent units, confirm both intake and exhaust are clear and the vent lengths and elbows match the manual.
Electrical Controls And Batteries
Intermittent pilot (IPI) systems use an electronic board and an ignition module. Weak batteries in a remote receiver or wall control can starve the module and drop the flame when the main burner opens. Replace all batteries as a set. Check wire spade connectors at the valve for a snug fit and clean contact. If a rocker switch feels loose or gritty, swap it; resistance adds up quickly in millivolt circuits.
When To Replace Parts
Thermocouple: Replace when the flame is correct yet the pilot releases as soon as you let go, or when the reading stays low with a clean blue flame.
Thermopile: Replace when the pilot holds yet the main burner drops out or won’t light, and loaded output is well below typical values.
Gas valve: Replace only after proving strong sensor output, tight wiring, correct gas supply, and sound venting.
Parts And Symptoms At A Glance
| Item | What It Does | Common Clues |
|---|---|---|
| Thermocouple | Holds pilot valve open on standing-pilot models | Pilot dies as soon as you release the control; low mV even with a sharp blue flame |
| Thermopile | Powers main valve and switch loop | Pilot holds but burner drops when you flip the switch; mV falls under load |
| ODS Pilot (vent-free) | Monitors room oxygen and trips on low O₂ | Unit shuts off after a few minutes; pilot lifts or sputters; improves with fresh air |
Care Tips To Keep The Pilot Lit All Season
Keep the glass and logs positioned as the manual shows; mis-placed logs can deflect the flame away from the sensor. Vacuum the firebox gently each fall. Replace remote and receiver batteries at the start of the heating season. Plan a yearly visit for gas-pressure checks, leak testing, and a full cleaning of the burner and pilot. For pilot appearance and placement notes, many manuals show photos and diagrams; see the sample guidance that “the pilot flame should just touch the top of the thermocouple tip” in the Hearth & Home log placement sheet.
Tool List For Safe DIY Checks
- Owner’s manual and lighting label
- Canned air and a soft brush
- Multimeter that reads DC millivolts
- Small flat screwdriver for pilot adjustment (model-dependent)
- Fresh AA/AAA batteries for remotes and modules
- Flashlight and a short insulated jumper wire
What To Do If The Pilot Still Won’t Stay Lit
You cleaned the pilot, confirmed a strong blue flame on the sensor, snugged connections, renewed weak switches, and replaced batteries. If the pilot still drops, schedule service. A technician can measure inlet and outlet gas pressure, test safety switches, read loaded millivolts at the valve, and replace the valve body if needed. That visit brings steady heat back on the next cold night.