High
Lock-out on Heatline Capriz 28

Your boiler has stopped working as a safety precaution because it either failed to light or became too hot.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Activated by overheat thermostat or ignition failure. Boiler has to be manually re-set by switching the control knob off (for 15 seconds) and on again.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

Related fault codes

F1View →F4View →

Related guides you might find useful

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →