Boiler keeps turning off or locking out
A boiler that lights and then shuts down within a minute or two is protecting itself. Something in the safety chain — flow, flame, pressure or airflow — is not happy.
Repeated lockouts are also the single biggest predictor of full failure within a heating season, so it is worth diagnosing properly rather than hitting reset every morning.
Try this first — free
Checks you can safely do yourself
Check pressure first
Below 0.5 bar and most boilers refuse to fire. Re-pressurise to 1.2 bar and see if the problem disappears.
Reset once — and only once
One reset is fine. If it locks out again, note the fault code and stop resetting; repeated resets on an ignition fault can flood the chamber.
Look at the flue outside
Blocked, iced up or full of leaves is a genuine cause, especially after a cold snap.
Feel your radiators
If only a couple get hot, poor circulation from sludge is making the boiler overheat and cut out. That is a powerflush job, not a new boiler.
Never remove the boiler casing or touch gas components yourself — that's illegal as well as dangerous. Anything behind the front cover is Gas Safe work.
If that didn't fix it
What it usually turns out to be
Low system pressure
Cheapest and most common. Usually points to a leak worth finding.
£99 – £180
Sludged system / poor circulation
Boiler short-cycles because it cannot dump heat into the radiators. A powerflush fixes it and protects the new warranty.
£450 – £650
Faulty flame sensing / ignition electrode
Boiler lights, loses flame signal, locks out.
£160 – £280
Failed pump
Overheat lockouts within a minute of firing.
£280 – £420
Fan or air pressure switch
Common on 8+ year old boilers.
£250 – £400
Prices inc VAT and include our £99 diagnostic. We confirm the price before any work starts — no surprises on the invoice.
Straight talk
When we'd tell you to replace instead
- You have had three or more lockouts in one season
- Two separate parts have already been replaced this year
- The boiler short-cycles even after a powerflush
- It is oversized for the house — very common in 2000s installs — and will never run efficiently
Repeated lockouts in December are how people end up with no heating on Christmas Eve. Get it diagnosed early.
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Frequently asked questions
Why does my boiler keep locking out?
A lockout is the boiler shutting itself down on a safety fault — usually flame loss, overheat, low pressure or a flue/airflow issue.
Is it safe to keep resetting?
One or two resets are fine. Persistent resetting on an ignition fault is not, and it will not fix the underlying cause.
Could it just need a powerflush?
Genuinely, yes — sludge causes far more overheat lockouts than people expect. We test the system water before recommending one.
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