Boiler Problems
Pilot Light Keeps Going Out? Causes and What To Do
Reviewed by our Gas Safe registered engineers · Last updated 21 July 2026
If your boiler has a permanent pilot light that won’t stay lit, it’s most often the thermocouple, a draught, or the gas supply. Newer combi boilers don’t have a pilot light — if yours doesn’t, our Not Igniting guide is the one you want.
Quick answer: The most common reason a pilot light won’t stay lit is a faulty thermocouple — the safety device that keeps gas flowing only while a flame is detected. Draughts, a dirty pilot jet, or a gas supply issue can also be to blame. Pilot lights are found on older boilers; modern combis use electronic ignition instead.
Common Causes
Why a pilot light won’t stay lit
These are the usual culprits, roughly in order. The colour on the left shows whether it’s a safe homeowner check or a job for a Gas Safe engineer.
| What happens | Likely cause | What to do |
|---|---|---|
| Won’t stay lit after releasing the knob | Faulty thermocouple | Needs an engineer to replace |
| Pilot lights then blows out | Draught near the flue or boiler | Check for draughts; keep the area around the boiler clear |
| Weak, yellow pilot flame | Blocked or dirty pilot jet | An engineer can clean or clear it |
| No pilot flame at all | Gas supply issue | Check other gas appliances; if none work, contact your supplier |
| Goes out repeatedly | Gas valve or flue fault | Book a Gas Safe engineer |
Safe Checks
What you can safely check
Safe to check
- Check for draughts near the boiler or flue that could blow the flame out
- Keep the area around the boiler clear and unobstructed
- Check other gas appliances are working (rules out a supply issue)
- Relight once, carefully following the boiler’s printed instructions
Stop and call us if…
- You can smell gas — leave the property and call 0800 111 999
- The pilot won’t stay lit after a couple of careful attempts
- The flame is yellow, or there’s soot around the boiler
Engineer Insight
What we usually find
On older boilers, a pilot that won’t stay lit is nearly always the thermocouple — an inexpensive, common part. We also check the pilot assembly and gas pressure, because a lazy yellow flame can point to a dirty jet or a supply issue rather than the thermocouple itself. If your boiler is a modern combi with no standing pilot, see our Boiler Not Igniting guide instead.
Costs
Typical pilot-light repair costs
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
Pilot light problems — your questions answered
What is a thermocouple?
It’s a safety device that senses the pilot flame and only lets gas flow while a flame is present. When it fails, the gas shuts off and the pilot goes out — a common, usually inexpensive repair.
Why won’t my pilot light stay lit?
Most often a failing thermocouple. Draughts, a dirty pilot jet or low gas supply can also stop it staying lit. An engineer can quickly identify which.
My boiler has no pilot light — why?
Modern combi and system boilers use electronic ignition and light on demand, so there’s no standing pilot. If yours won’t fire, see our Boiler Not Igniting guide.
Is it safe to keep relighting the pilot?
Relighting once, following the boiler’s instructions, is fine. If it won’t stay lit after a couple of attempts, stop and book an engineer — and if you smell gas, leave and call 0800 111 999.
How much does it cost to fix a pilot light?
A thermocouple replacement is typically £90–£180 in North London including labour. You’ll always get an upfront quote first.
Related
Keep troubleshooting
For combi boilers with electronic ignition rather than a pilot.
Read guideBoiler ProblemsBoiler Not Turning OnNo response at all — power, pressure and thermostat checks.
Read guideMaintenanceSigns Your Boiler Needs ServicingPilot and flame issues are one sign a service is overdue.
Read guideEmergencyBoiler Breakdown Emergency GuideWhat to do first if you’ve lost heat or smell gas.
Read guideFault CodesBoiler Fault Code LibraryLook up the exact code by brand if one is showing.
Browse codesBoiler ProblemsBoiler Problems HubAll our boiler troubleshooting guides in one place.
Browse guidesBrowse all Boiler Problems guides, or head back to the Help & Advice Centre.
Pilot won’t stay lit? We’ll sort it.
Book a Gas Safe engineer to replace the thermocouple or check the gas supply, or call and tell us what the pilot’s doing — we’ll give you an honest steer first.
Gas Safe Registered 918817 | North London specialists | Upfront pricing