Boiler lockout: what the reset button does, and when to stop pressing it
Last reviewed · owner Mike Fellows · general information, not legal advice
A lockout is the boiler deliberately shutting down because a sensor saw something wrong: low pressure, a failed ignition, overheating, or a blocked flue or condensate pipe. Check the display code against your manual, fix the obvious causes you can (pressure, a frozen condensate pipe), then reset once. A boiler that locks out again is telling you the fault is still there; repeated resets are how small faults become big ones. Gas faults are Gas Safe engineer work only.
What is a boiler lockout?
A protective shutdown. The boiler's controls detected a condition outside safe limits and stopped the appliance rather than run through it. The display usually shows a fault code, and the code matters: it says whether you are looking at pressure, ignition, overheat or flue trouble, and your manual translates it.
What can I safely check before resetting?
Three things. The pressure gauge: below about 0.8 bar, re-pressurise first. The condensate pipe in freezing weather: a frozen external condensate pipe is one of the most common winter lockouts, and thawing it with warm, not boiling, water clears it. And the obvious: is the gas supply on, has a prepayment meter run out, has power tripped. Then press reset once and let the boiler run its sequence.
When should I stop pressing reset?
After the second lockout. A boiler that keeps locking out has a real fault, and every forced restart stresses the parts involved. Note the fault code, stop resetting, and book a Gas Safe registered engineer; by law, only a Gas Safe registered engineer may work on the gas side of the appliance. If you ever smell gas, do not touch the boiler at all: call the National Gas Emergency line on 0800 111 999.
Sources
- HSE, Gas health and safety in the home (accessed 2026-09-05)
- GOV.UK, Report a gas emergency (accessed 2026-09-05)
This page is general information for property professionals, not legal advice. For a decision that matters, take advice on your specific facts.
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