BoilerFaultCodesPilot light keeps going out on your boiler?
Pilot lights are a feature of older, pre-2005 boilers (and a few floor-standing models). Modern condensing boilers use electronic ignition and don't have a pilot at all. If yours won't stay lit, here's what's usually happening — and whether it's worth repairing or replacing.
A pilot light fault is often the sign
A boiler with a pilot light is typically 20+ years old and running at 65–70% efficiency (vs 90%+ on a modern A-rated boiler). Running cost difference is often £200–£400 a year. Before spending £300 on parts, check the cost of a new boiler.
Five causes ranked by how common they are
Draught blowing the flame out
The most common cause. A window left open, extractor fan pulling air, or a draughty flue. Easy to confirm: close all windows, turn off extractors, try again. If it stays lit, you've found your answer.
Fix: Seal any obvious draughts near the boiler. A flue draught guard may be needed — that's an engineer job.
Worn thermocouple
The thermocouple is a safety device that detects whether the pilot flame is actually burning. If it's worn, it doesn't sense the flame and shuts off the gas supply — even though the flame is lit. Very common on boilers over 10 years old.
Fix: Thermocouple replacement: £100–£180 fitted. Quick job for a Gas Safe engineer.
Dirty / fouled pilot burner
Dust, soot or spider webs inside the pilot assembly stop the flame burning cleanly. Usually happens on older back-boilers and floor-standing models.
Fix: Cleaning is part of an annual service. If it's overdue, book one — around £80–£120.
Gas supply issue
Low gas pressure — often because another appliance is running, or the meter regulator is partly blocked. Try the pilot when no other gas appliances are running.
Fix: Gas Safe engineer to check working pressure. Rarely a DIY fix.
Faulty gas valve
The gas valve regulates the supply to the pilot. Worn valves don't hold pressure properly. Less common but serious.
Fix: Gas valve replacement: £250–£450 fitted.
Never do these
- › Don't keep relighting if it goes out within seconds — gas is escaping each time
- › Don't tamper with the thermocouple or gas valve yourself — gas work must be Gas Safe
- › Don't use matches or lighters near a suspected gas smell
- › Don't override the shutoff — it's there for your safety