You hold the knob down, the pilot lights, everything looks fine — then you let go and the flame dies. Light it again, same result. On the older standing-pilot furnaces and the wall and floor furnaces so common in Bay Area homes, a pilot that lights but won't stay lit is one of the most frequent no-heat calls, and there's a clear leader among the causes: a worn-out thermocouple. A few other faults can do it too, and one of them is a reason to stop and call the gas company.
This page walks through why a pilot won't hold, what's safe to try once yourself, and when it's time for a licensed tech — because this is gas.
How it usually shows up:
- You light the pilot and hold the knob; it burns, then goes out the moment you release it.
- The pilot stays lit while you hold the button but drops out seconds later.
- The wall or floor furnace won't fire its main burner because the pilot keeps dying.
- The pilot flame looks weak, small, or yellow and orange and seems to drift or flicker.
A gas-safety note first
This is a gas appliance. If you smell gas — a rotten-egg odor — do not try to relight anything. Leave the house and call your gas utility (or 911) from outside. Don't relight over and over, either — repeated attempts let unburned gas build up. Relight once by the plate instructions, and if it won't hold, stop and call a tech.
Why your pilot light won't stay lit
Match the symptom to the likely cause:
- A bad thermocouple — the number-one cause. The thermocouple is a small probe sitting in the pilot flame. Its job is to sense heat and tell the gas valve "the pilot is lit, keep the gas on." When it's worn out, it stops sensing the flame, so the valve shuts the gas the instant you release the knob and the pilot dies.
- A dirty or clogged pilot orifice. Dust, lint, or corrosion narrows the tiny opening, so the pilot flame is too small and weak to properly heat the thermocouple.
- A weak or drafty pilot flame. A small flame, or one being pushed around by a draft, doesn't bathe the thermocouple in steady heat — same result, the valve closes.
- A failing gas valve. If the valve's pilot safety circuit is faulty, it won't hold the gas open even when the thermocouple is working.
- A dirty flame sensor (on newer units). Electronic-ignition furnaces don't use a standing pilot, but a comparable fault — a grimy flame sensor that can't confirm the flame — makes the burner light and then shut right back down.
The usual fix
On a standing-pilot furnace or wall heater, our tech confirms the pilot flame is clean and strong, then tests the thermocouple's output — a weak or dead thermocouple is the common, affordable replacement. If the pilot itself is weak, the pilot assembly and orifice get cleaned or replaced, and any draft is addressed. If the thermocouple and pilot are good but the valve won't hold, the gas valve is the fix. On newer units it's usually a flame-sensor cleaning. You get a firm quote before any part goes in.
DIY vs. calling a pro — the honest version
Safe to check yourself first (free):
- Relight the pilot once, exactly per the instructions printed on the unit — hold the knob the full time it specifies before releasing.
- Look at the flame. A healthy pilot is mostly blue and wraps firmly around the thermocouple tip. Weak, yellow, or drifting is a clue.
- With the gas off and the unit cool, gently clear visible dust or lint from around the pilot area — never poke the orifice with anything metal.
- Check for obvious drafts blowing across the pilot from a nearby vent or window.
Call a pro when:
- The pilot won't stay lit after one proper relight — the classic thermocouple failure.
- The pilot is weak or won't clean up, or the burner lights then shuts right off.
- You suspect the gas valve isn't holding.
- Any gas smell — leave first, call the utility, then have a tech out.
Thermocouples, pilot assemblies, and gas valves are gas-safety parts. This is where a licensed tech pays for itself and keeps the appliance safe.
What it costs in the Bay Area
For wall and floor furnaces the price follows the part, and the common ones are affordable. A thermocouple runs about $80–$280 — the usual fix for a pilot that won't hold. A pilot assembly is roughly $100–$320 when the pilot itself is weak or clogged, and a gas valve runs about $150–$450 when the valve won't keep the gas open. We charge a diagnostic fee that's credited toward the repair when you approve the work, and you'll always see a flat, upfront price before we start.
Get your heat working safely
Triton services older standing-pilot furnaces and the wall and floor furnaces found throughout the Peninsula and East Bay — Alameda, San Leandro, San Mateo, Redwood City, Burlingame, Menlo Park, San Carlos, and Belmont, where plenty of homes still run these classic heaters. A pilot that won't hold is usually a small, safe fix once a tech has eyes on it. See our full HVAC repair hub for everything we cover.
Book online or call (888) 993-5699. We'll get the pilot holding and the heat back on — safely.
Related pages
- HVAC Repair in the SF Bay Area — our full heating & cooling hub
- Wall Furnace Not Working — the wall & floor furnace hub
- Furnace Won't Ignite — the electronic-ignition version
- Furnace Not Heating — no-heat diagnosis
- HVAC & Heating Repair in Alameda — East Bay service area
Frequently asked questions
Why won't my furnace pilot light stay lit? The most common reason is a worn-out thermocouple — the probe that senses the pilot flame and tells the gas valve to stay open. When it fails, the valve shuts the gas the moment you release the knob and the pilot dies. A weak or dirty pilot flame, a clogged pilot orifice, or a failing gas valve can cause the same thing. If it won't hold after one proper relight, it needs a tech.
What is a thermocouple and why does it make the pilot go out? A thermocouple is a small metal probe that sits in the pilot flame and generates a tiny electrical signal from the heat. That signal tells the gas valve the pilot is burning, so it's safe to keep the gas on. When the thermocouple wears out it stops sending that signal, so the valve closes for safety and the pilot goes out. Replacing it is the usual, affordable fix.
Is it safe to keep relighting a pilot that won't stay lit? Relight once, carefully, by the instructions on the unit. Don't relight over and over, because repeated attempts let unburned gas accumulate. And if you smell gas at any point, stop, leave the house, and call your gas utility from outside before doing anything else. A pilot that won't hold after one relight should be handled by a tech.
Can I clean the pilot myself? With the gas off and the unit fully cool you can gently clear visible dust or lint from around the pilot and check for a draft blowing across it. Don't poke the small orifice with a metal object — that can damage it. If cleaning the area doesn't give you a strong, steady blue flame that holds, the thermocouple or pilot assembly likely needs a tech.
How much does it cost to fix a pilot light that won't stay lit in the Bay Area? For wall and floor furnaces, a thermocouple is about $80–$280, a pilot assembly $100–$320, and a gas valve $150–$450, so the common fixes are on the affordable end. We credit the diagnostic fee toward the repair when you approve the work and give you a firm price before any work begins.
Do you repair old wall and floor furnaces? Yes — we service the older standing-pilot furnaces and the wall and floor furnaces common across the Peninsula and East Bay, including Alameda, San Leandro, San Mateo, Redwood City, Burlingame, and Menlo Park. Call (888) 993-5699 to book, or if you smell gas, leave first and call your gas utility.