Why Won’t My Gas Fireplace Pilot Light Stay Lit?

Texas Chimney Experts — chimney and fireplace inspection specialists for DFW. Free inspection, written quote before any work, no surprise fees.

A pilot that will not stay lit is one of the most frequent gas-fireplace calls we log from Tarrant, Parker, and west Denton counties (west of I-35). The sequence below is what our techs run on-site — work through it yourself before paying for a service call.

A pilot that lights, then dies within seconds of releasing the control knob, points almost always to a failing thermocouple (single-pilot system) or thermopile (millivolt system). Rarer causes: a dirty pilot orifice, a draft pushing the flame off the sensor, or a failing gas valve. Thermocouple or thermopile replacement is a 30-minute fix. A gas valve is a bigger job.

Gas fireplaces installed 10+ years ago — standard in early-2000s Plano, Frisco, and McKinney builds — sit squarely inside the thermocouple-failure window now. Pilot complaints also spike in winter, when our cold fronts drop attic temperatures and older gas lines pick up minor moisture issues.

⚠ Safety first

Code-relevant safety notice: a gas fireplace is a fuel-burning appliance with strict requirements for combustion-air supply, gas pressure, and venting. Any gas smell — however faint — means leave the area, operate no electrical switches, and call your gas utility's emergency line. Never attempt a repair you are not confident performing.

Work the steps in sequence, one at a time. Each closes with a stop-check that tells you whether the finding is conclusive or you keep going.

• 1. Confirm and time the failure — Light the pilot per the fireplace manual, holding the control knob in for the full 30-60 seconds it specifies, then release and time how long the flame lasts. (Dying within seconds = a sensor problem, thermocouple or thermopile. Staying lit a while before it quits = a different cause — dirt or draft. If this fixes it: STOP. If not: continue.)
• 2. Examine the pilot flame — A healthy pilot burns steady and blue and wraps the tip of the thermocouple/thermopile sensor. A yellow, weak, or misaligned flame that misses the sensor is your finding. (An underheated sensor never signals the gas valve to hold open. If this fixes it: STOP. If not: continue.)
• 3. Clean the pilot orifice — Shut the gas at the shut-off valve and wait 5 minutes. Clear any visible dust or web debris from the pilot assembly with a soft brush or compressed air. Spider webs in the orifice turn up surprisingly often — a pest called the gas-line spider nests in them specifically. (A cleaned orifice sometimes ends the problem outright. If this fixes it: STOP. If not: continue.)
• 4. Test for drafts at the pilot — Open the fireplace front and hold a lit match near the pilot area. Constant disturbance of the match flame documents a draft pulling the pilot off the sensor — a missing or cracked glass front on a direct-vent unit is the usual cause. (Correct the draft first — replace the gasket, reseat the glass — before buying parts. If this fixes it: STOP. If not: continue.)
• 5. Meter the thermocouple or thermopile (if you own a multimeter) — With the pilot lit and held, a sound thermocouple reads 25-35 mV across the connection; a thermopile reads 300-750 mV. Readings below those ranges mean the part is failing. (An out-of-range reading confirms replacement. If this fixes it: STOP. If not: continue.)
• 6. Replace the failing sensor — The thermocouple or thermopile is a $30-$-+ part and a 30-minute job for someone at ease with gas appliances. If that is not you, this is precisely where a pro belongs — gas work punishes a single missed step. (A new part, properly seated, should hold the pilot; if not, suspect the gas valve. If this fixes it: STOP. If not: continue.)
• 7. Suspect the gas valve last — A failing gas valve — the brass body the thermocouple feeds into — means the sensor works but the valve no longer holds open. At $250-$-+ for the part plus labor, this is strictly professional territory. (A failed valve means scheduled gas-fireplace repair, not DIY. If this fixes it: STOP. If not: continue.)

When to call a pro

When the sequence does not isolate the fault, book a Level 2 inspection to NFPA 211. Texas Chimney Experts carries CSIA certification and covers Tarrant, Parker, and west Denton counties west of I-35 — every inspection report is camera-documented.

Call (214) 444-8103, or request your written quote online.

Current DFW market ranges. A written quote precedes any repair work — no hidden fees, no verbal estimates.

How long should a thermocouple last?

8-12 years is typical. It is a wear part — the sensor metal degrades a little with every heat cycle. An original unit past the 10-year mark is a reasonable candidate for preventive replacement.

Why does the pilot work in winter but not summer (or vice versa)?

Temperature changes gas pressure and combustion-air density. A marginal system passes in one season and fails in the other — which usually means a borderline part worth replacing now, rather than waiting on a complete failure.

Is a yellow pilot flame dangerous?

A yellow pilot documents incomplete combustion: more carbon monoxide, more soot. It also signals a sensor that is not being heated properly. Fix it — do not run the fireplace on a yellow pilot.

Can I replace the thermocouple myself?

Yes, provided you are comfortable around gas appliances, can shut the gas off at the valve, and follow the manufacturer manual to the letter. Any hesitation on those three points, and the $150-$-+ service call is money well spent.

Why does my pilot light only go out at night?

A draft, most likely. Cooler night temperatures, a tighter house, and shifting wind direction combine into a downdraft that daytime conditions never produce. Check envelope sealing around the fireplace chase.

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Book a Level 2 inspection — the written, photo-documented report is back within 24 hours. Call (214) 444-8103 or use the contact form.

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