Gas logs going out point to pilot, sensors, air supply, or fuel issues—start with the pilot flame and safety sensors.
Gas log won’t stay lit: quick checks that save time
Start with basics. Is the gas valve open, the shutoff inline handle parallel with the pipe, and the appliance switch set to on? If you smell gas, stop and call a licensed fitter. Next, look at the pilot. A steady blue flame with a small yellow tip should bathe the thermocouple or thermopile. If the flame is tiny, split, or waving, the safety circuit may drop and the burners shut off.
Dust and spider webs in the pilot air inlet change the flame shape. A soft brush and short bursts of canned air aimed at the pilot hood and air holes often restore a healthy flame. Do not poke the orifice with wire, which can damage it. Relight and hold the control knob down long enough for the sensor to heat up. Many units need 30 seconds or more.
Common causes and what to try first
Most outages relate to flame sensing and airflow. Use the table below to match a symptom with fast actions. Work with the gas off and the system cool before any cleaning.
| Symptom | Likely cause | First steps |
|---|---|---|
| Pilot lights but goes out | Weak pilot or dirty thermocouple | Clean pilot, align flame to tip, hold knob longer |
| Burners light then stop | Thermopile under-heated or loose wires | Tighten connections, clean pilot, run in CPI if available |
| Unit won’t light on cold days | Cold-start lockout or draft | Switch to continuous pilot, warm the firebox, retry start |
| Flame lifts or sputters | Low gas pressure or wind in vent | Verify other gas appliances, shield outdoor winds, call utility if widespread |
| Vent-free set shuts down | Oxygen depletion sensor reacting | Open a window a crack, clean ODS air inlet, remove candles or aerosols nearby |
Why gas logs go out mid-burn
Gas log sets and fireplaces use safety parts that watch the flame. If the sensor cools, the valve shuts. A thermocouple serves standing pilots, and a thermopile feeds millivolts to the control circuit. On electronic systems, a flame rod proves flame. Any drop in pilot size or aim cools the sensor and trips shutdown.
Room air matters too. Vent-free sets include an oxygen depletion sensor that turns off gas if oxygen drops near 18 percent. Scents, aerosols, and dust near the pilot can disturb that tiny flame. Direct-vent models depend on clear intake and exhaust paths, so snow, nests, or a misaligned cap can choke airflow and starve the flame.
Safe step-by-step: ten-minute triage
1) Turn the control to off and let the unit cool. 2) Confirm the manual shutoff valve is open. 3) Remove the glass (if applicable) per the manual. 4) Vacuum gently around the pilot and burner. 5) Use canned air at the pilot hood and the small air slots. 6) Check that the pilot flame will touch the top third of the sensor. 7) Relight and hold the knob in for at least 30 seconds. 8) If the pilot now stays lit, run the main flame. 9) If the main flame drops, tighten low-voltage spade plugs at the valve. 10) If the pilot still quits, stop and schedule service.
Pilot flame: what healthy looks like
A good pilot looks crisp and mostly blue. The tip of the flame should kiss the thermocouple or wrap the thermopile. A lazy yellow flame means too little air; a hard, noisy flame can mean too much air. Both conditions over-cool the sensor and lead to dropout. Some brands let you tweak pilot rate with a small screw on the gas valve. Small turns only, and never wrench on the orifice.
Electronic ignition quirks you can fix
Intermittent-pilot systems light the pilot each time. Cold enclosures can slow start-up. Many makers provide a switch that keeps the pilot on in cold weather, labeled CPI, CP, or SureFire. Running the pilot steadily warms the firebox and keeps the thermopile ready. If your system locks out, kill power for a minute, then try again with the glass in place to prevent drafts.
Vent-free sets: special notes
Vent-free log sets burn room air and must stay clean. The oxygen sensor sits in the pilot and is tuned for a narrow air mix. Use compressed air to clear lint at the air intake and the pilot hood. Avoid household cleaners and candles near the set during lighting. Crack a nearby window if the room feels stuffy, pets are many, or a range hood is running.
For safety reminders on carbon monoxide alarms and seasonal checks, see the U.S. Consumer Product Safety Commission guidance. Manufacturer guides from brands like Regency and HHT manuals explain start-up modes and pilot tips you can use.
Gas supply and pressure basics
Natural gas and propane units both need steady pressure. If other appliances flicker or won’t start, the supply may be low. For propane, check that the tank has fuel and the regulator is free of frost. A frozen regulator starves the pilot and the main burner. At the fireplace, check for a sediment trap or drip leg before the valve; if debris gathers there, flow drops. Do not disassemble piping; this is a job for a license holder, but you can note patterns and share them with service.
Compare performance at different times of day. If the flame weakens when a clothes dryer or a big range is running, that clue points to supply limits. A gas utility or propane supplier can confirm delivery pressure at the meter or tank, which removes guesswork.
Draft and vent checks that matter
Direct-vent models breathe through a coaxial pipe. The inner tube carries exhaust and the outer ring brings in air. If the cap sits crooked or the outer ring is blocked by leaves, the pilot can lift and drop out. From outside, make sure the cap is level, the louvers are clear, and no bird screen is clogged. Wind baffles on some caps can loosen; a small tilt can disturb airflow.
Inside the room, the glass must seal tight. A chipped gasket or hair across the seal lets room air rush in and upset the flame. Clean the gasket with a dry cloth and seat the glass evenly. Never run with the glass removed unless the manual says it’s okay for that model.
Log placement and ember bed setup
Logs do more than look nice. They steer flame and shape heat around the pilot. If a log is out of place, flame impinges on it and the pilot loses heat. That’s when you see the main burner drop and relight over and over. Use the placement diagram from your manual and match pins, notches, and tabs. Move one piece at a time, then check the pilot view.
Fresh ember wool can brighten the look, but too much over ports smothers the flame. Keep ember material light and fluffy, and away from pilot parts. Replace ember material only with the maker’s approved type.
Thermocouple vs thermopile: quick guide
A thermocouple is a thin probe that makes a small voltage when heated by the pilot. That signal holds open a safety valve for a standing pilot. A thermopile is a larger bundle that makes more voltage to run controls and open the main valve. If a standing pilot drops, think thermocouple heat or alignment. If the pilot stays but the main flame quits, think thermopile strength or wiring.
Owners can clean the tips and tighten spade terminals. Meter testing belongs to a pro, since readings change with load and heat. If the tip looks eroded, or the sheath is cracked, ask for replacement with the correct part number.
When to call a pro
Stop DIY work now if you see soot inside a sealed firebox, smell gas, find water in the firebox, or the pilot blows out the instant you release the knob. These point to venting faults, valve issues, or pressure problems. Licensed service has the tools to read pressures and test safety circuits.
Deeper fixes many owners skip
Loose wiring at the gas valve causes dropouts when the main flame starts. Push each spade plug fully home. Corroded battery trays in remotes or receivers cause erratic starts; replace with fresh alkaline cells. Dirty burner ports can make the flame lift away from the sensor; brush the ports and vacuum the pan.
Symptom-to-cause map for fast tracking
Use this quick map when you need to sort a tricky outage after basic cleaning and relighting. Today.
| What you see | Likely cause | Action plan |
|---|---|---|
| Pilot flame mostly yellow | Clogged air intake | Clean pilot, check ODS air holes |
| Pilot strong but main drops | Weak thermopile output | Warm in CPI mode, clean pilot, check connectors |
| Shuts off after 5–15 minutes | Overheating or draft reversal | Confirm cap position, clear intake/exhaust, check fan operation |
| Clicks, no ignition | No spark or no gas | Check power, verify gas valve on, inspect ignitor gap through glass |
| Only lights with glass off | Sealed path leak or misfit glass | Reseat glass, check gasket, call service for pressure test |
What to tell service
When you book a visit, share the make and model, fuel type, venting style, and how the shutdown happens. Say whether the pilot drops first or the main flame quits while the pilot stays on. Note fan use or wind at the cap. Tell them how long the unit runs before it stops and what you tried—cleaning the pilot, reseating glass, or running in CPI. Solid details help the tech bring the right parts.