Why Won’t My Gas Fireplace Pilot Light Stay Lit? | Prime Chimney Exper
Prime Chimney Experts — DFW chimney & fireplace specialists. Free inspection, written quote, no surprise fees.
If you’ve noticed this in your home, you’re not alone: why won’t my gas fireplace pilot light stay lit is one of the most common questions we get from Southlake, Westlake, Colleyville, Highland Park homeowners. Below is the diagnostic flow we use on-site, written so you can run it yourself before you spend money on a service call.
TL;DR — What we typically find
If the pilot lights but goes out within seconds of releasing the control knob, the cause is almost always a failing thermocouple (single-pilot system) or thermopile (millivolt system). Less commonly: a dirty pilot orifice, a draft blowing the flame off the sensor, or a failing gas valve. The thermocouple/thermopile is a 30-minute fix; gas valve replacement is a bigger job.
Why we see this in DFW
DFW homes with gas fireplaces installed 10+ years ago — common in early-2000s Plano, Frisco, McKinney builds — are right in the thermocouple-failure window now. We also see pilot issues spike in winter when our cold fronts drop attic temps and old gas lines develop minor moisture issues.
⚠ Safety first
A note from our team — please read first: Gas fireplaces involve a fuel-burning appliance and require correct combustion-air supply, gas-pressure, and venting. If you smell gas at any point — even faintly — leave the area, do not operate any electrical switches, and call your gas utility’s emergency line. Do not attempt repairs you’re not confident in.
Diagnostic flow — work through in order
Run these steps one at a time. Each step ends with a stop-check so you know whether to keep going or call us.
- 1. Confirm the problem first — light it and time it — Light the pilot per the fireplace manual. Hold the control knob in for the full 30-60 seconds the manual specifies, then release. Time how long until it goes out. (Out within seconds = sensor problem (thermocouple/thermopile). Stays lit a while then dies = different issue (dirt, draft). If this fixes it: STOP. If not: continue.)
- 2. Check the pilot flame visually — A healthy pilot flame is steady, blue, and wraps around the thermocouple/thermopile sensor tip. Yellow, weak, or flame that doesn’t touch the sensor = your problem is here. (Weak/yellow/misaligned flame = sensor isn’t getting heated properly, so it doesn’t signal the gas valve to stay open. If this fixes it: STOP. If not: continue.)
- 3. Clean the pilot orifice — Turn off the gas at the shut-off valve. Wait 5 minutes. With a soft brush or compressed air, clean any visible dust or spider-web debris from the pilot assembly. Spider webs in the orifice are surprisingly common (pest called gas-line spiders specifically nests in them). (Dirty orifice cleaned = sometimes that’s the whole fix. If this fixes it: STOP. If not: continue.)
- 4. Check for drafts on the pilot — Open the fireplace front. Light a match near the pilot area. If the match flame is constantly disturbed, you have a draft pulling the pilot off the sensor. Common cause: a missing or cracked glass front on a direct-vent unit. (Visible draft = fix the draft (replace gasket, reseat glass) before replacing parts. If this fixes it: STOP. If not: continue.)
- 5. Test the thermocouple/thermopile (if you have a multimeter) — With pilot lit and held, a healthy thermocouple reads 25-35 mV across the connection. A thermopile reads 300-750 mV. Below those ranges = part is failing. (Out-of-range reading confirms the part needs replacement. If this fixes it: STOP. If not: continue.)
- 6. Replace the thermocouple or thermopile — This is a $30-$-+ part and a 30-minute job for someone comfortable with gas appliances. If you’re not, this is exactly when to call a pro — gas-related work where one missed step matters. (Part replaced + secured = pilot should stay lit. If not, the gas valve itself may be failing. If this fixes it: STOP. If not: continue.)
- 7. If it still won’t stay lit, the gas valve is suspect — A failing gas valve (the brass body the thermocouple feeds into) means the sensor is working but the valve no longer holds open. This is a $250-$-+ part plus labor and is firmly pro-only territory. (Failed gas valve = scheduled gas-fireplace repair, not DIY. If this fixes it: STOP. If not: continue.)
When to call a pro
When the home-checks above don’t resolve it, our concierge team handles the rest end-to-end. Prime Chimney Experts serves Southlake, Westlake, Colleyville, Highland Park, and surrounding luxury enclaves — single-point-of-contact, white-glove visit, full disclosure on every line item.
What it costs to diagnose & fix (DFW, 2026)
Real DFW market ranges. Inspection always comes with a written quote before any repair work begins — no hidden fees.
| Service | Typical range |
|---|---|
| Level 1 inspection (gas fireplace diagnostic) | $89 |
| Pilot orifice cleaning + adjustment | $100-$-+ |
| Thermocouple replacement | $150-$-+ |
| Thermopile replacement | $200-$-+ |
| Gas valve replacement | $400-$-+ |
| Full gas system inspection (any leak signs) | $199-$-+ |
Frequently asked questions
How long should a thermocouple last?
Typically 8-12 years. They’re a wear part — the sensor metal degrades with each heat cycle. If yours is original and 10+ years old, replacing it preventively is reasonable.
Why does the pilot work in winter but not summer (or vice versa)?
Temperature affects gas pressure and combustion-air density. Marginal systems work in one season and fail in the other. This usually means a part is borderline and worth replacing rather than waiting for a full failure.
Is a yellow pilot flame dangerous?
Yellow pilot indicates incomplete combustion, which means more carbon monoxide and soot. It’s also a sign your sensor isn’t getting properly heated. Address it — don’t run the fireplace with a yellow pilot.
Can I replace the thermocouple myself?
If you’re comfortable with gas appliances, can shut off gas at the valve, and follow the manufacturer manual exactly — yes. If any of that gives you pause, this is a $150-$-+ service call worth paying.
Why does my pilot light only go out at night?
Likely a draft. Cooler nighttime temps + tighter house + wind direction create downdraft that the daytime conditions don’t. Look for envelope sealing issues around the fireplace chase.
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Reach our concierge desk to schedule a discreet, scheduled visit at a time that suits the household. Call (682) 226-6257 or use the contact form.
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