Boiler has locked out — how to reset it correctly

A boiler lockout is a safety feature — the boiler detected a fault and shut itself down to prevent damage or danger. It is not always a serious problem, but do not just keep resetting without investigating.

Note the fault code on the display before resetting — take a photo. Enter it in our Boiler Fault Code tool to understand what the boiler detected.

Press and hold the reset button (usually a flame symbol or "Reset") for 3 seconds. The boiler will try to restart. Stand and watch it for 2 minutes.

If the boiler restarts successfully and runs normally: check the pressure gauge (top up if below 1 bar), note the fault code, and monitor for 24 hours. A one-off lockout after a power cut or pressure dip is normal.

If the boiler locks out again within minutes or hours of the reset, do not reset it more than twice. Repeated resets without fixing the underlying fault can: prime the combustion chamber with gas (fire risk), damage the boiler components, and void your warranty.

Common causes of lockout that require an engineer: faulty igniter or electrode, failed gas valve, faulty PCB, blocked heat exchanger, frozen condensate pipe (in winter), or a gas supply issue.

A condensate pipe freeze is a common lockout cause in cold weather — the condensate pipe from the boiler to the drain can freeze. Look for a plastic pipe (usually white) exiting through an external wall at low level. Thaw it with warm (not boiling) water.