Boiler Pilot Light Keeps Going Out
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Post a job — we'll find you an engineer →Only attempt to relight the pilot light following the boiler manufacturer's instructions. If you smell gas at any point, stop and call 0800 111 999.
A pilot light that won't stay lit is one of the most common heating problems UK homeowners face, particularly with older boiler models. It's frustrating when you've got the heating on but the flame keeps extinguishing itself — leaving you without hot water and central heating. The good news is that it's rarely a sign of catastrophic boiler failure; in most cases, it's down to a worn thermocouple, a draught problem, or an issue with your gas supply. This guide walks through the practical checks you can do yourself, from testing other gas appliances to relighting the pilot following your boiler's own instructions. However, if the pilot won't stay lit after a couple of attempts, or if you smell gas, it's time to call a Gas Safe registered engineer rather than risk safety or cause further damage.
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Most likely cause & what to check
Check if other gas appliances in your home are working (cooker, gas fire). If none work, the problem may be with the gas supply — check you have credit on a prepayment meter or call your gas supplier.
Try relighting the pilot light following the instructions on your boiler's casing. Most modern boilers have an ignition button — hold it for 30–60 seconds after the flame appears.
If the pilot lights but goes out when you release the button, the thermocouple is almost certainly faulty. The thermocouple is a safety device that detects the pilot flame and keeps the gas valve open — when it fails, it cuts the gas.
Check for draughts near the boiler. If your boiler is in a draughty cupboard or the flue cover is missing, wind can extinguish the pilot. This is less common on modern sealed flue boilers.
If the pilot repeatedly fails to light or goes out immediately, do not keep trying. Call a Gas Safe registered engineer — attempting to bypass safety devices is illegal and dangerous.
A thermocouple replacement typically costs £80–150 including labour and is a straightforward repair for a Gas Safe engineer. Do not attempt this yourself.
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Frequently asked questions
How often should a boiler pilot light stay lit once relit?
A healthy pilot light should stay lit indefinitely once you've released the ignition button — it's designed to burn continuously. If it goes out within minutes or hours, something's wrong, whether that's a faulty thermocouple, a gas supply issue, or a draught problem. Don't keep relighting it repeatedly; after two or three failed attempts, call a Gas Safe engineer.
Is it safe to keep trying to relight the pilot myself?
It's safe to follow the manufacturer's relighting instructions once or twice, but repeatedly attempting to relight an unreliable pilot can lead to gas accumulation in the combustion chamber. If it fails to stay lit after a couple of attempts, stop and call a registered engineer — this is both a safety issue and a legal requirement.
Could a pilot light going out mean my boiler is about to break down?
Not necessarily — a faulty thermocouple is a cheap, straightforward repair that doesn't indicate wider boiler problems. However, if your boiler is very old (15+ years) and experiencing repeated issues, it may be worth considering a replacement rather than stacking up repair costs.
What's the difference between a pilot light and an ignition system on newer boilers?
Older boilers use a continuously burning pilot light that needs a thermocouple to stay lit; newer boilers often have electronic ignition systems that light the main burner on demand without a standing pilot. If your boiler has no visible pilot light, it likely uses electronic ignition, and the fault-finding approach will be different — a Gas Safe engineer should diagnose this.
Can I replace the thermocouple myself to save money?
Legally, you cannot — thermocouple replacement on a gas boiler must be carried out by a Gas Safe registered engineer. Attempting this yourself voids your warranty, breaches gas safety regulations, and risks creating a dangerous installation. The repair cost (typically £80–150 including labour) is worth paying for safety and peace of mind.
Should I turn off my boiler if the pilot light won't stay lit?
Yes, once you've established it's a fault. Switch it off at the control dial and leave it off until a Gas Safe engineer can assess it. This prevents repeated failed ignition attempts and any potential gas accumulation in the system.