Why Does My Boiler Keep Turning Off?

The difference between normal cycling and a genuine fault, the common causes of lockouts, and why you should stop resetting it.

Last updated: 2026-10-19

A boiler switching off occasionally is normal. A boiler that keeps locking out is telling you something is wrong — and repeatedly pressing reset does not fix it.

Normal cycling vs a fault

Modern boilers modulate: they turn the burner down and off as the room reaches temperature. That is normal and you may barely notice it. A fault looks different — the boiler stops mid-demand, the display shows a fault code, and it will not restart until reset (or not at all).

Common causes of repeated cut-outs

• Low pressure — the most common and easiest to check. See how to repressurise.
• Condensate pipe frozen — in cold snaps, the plastic condensate pipe can freeze and block, causing a lockout. A visible white pipe outside is the usual suspect.
• Blocked or restricted condensate trap — causes intermittent lockouts.
• Overheating — often a circulation problem: a failing pump, a stuck valve, or sludge restricting flow.
• Ignition or flame detection faults — the boiler tries to light and fails.
• Flue or air pressure switch faults — the boiler will not run safely without correct flue operation.
• Sensor faults — temperature sensors giving incorrect readings.
• Gas supply issues — low gas pressure or a supply problem.

Why you should stop resetting it

A lockout is a safety response. Resetting a boiler that repeatedly locks out can mask a fault — for example, a flue problem or a flame that is not proving correctly. If it locks out twice, stop and book an engineer rather than resetting a third time.

Never remove the casing or attempt to clean or adjust anything inside the boiler.

Frost and condensate

If it is freezing and the boiler has locked out, check whether the white condensate pipe outside has frozen. Some boiler manuals describe a safe thawing method using warm water — follow the manufacturer’s instructions only, and never use boiling water or a naked flame. If you are unsure, call an engineer.

When to call

Book a boiler repair visit if the boiler locks out repeatedly, shows a fault code, or will not restart. Note the code and how often it happens — that history genuinely speeds up diagnosis.

If you smell gas at any point, call the National Gas Emergency Service on 0800 111 999 immediately.