High Lockout
Neon4 on Glow-worm Ultimate

Your boiler is attempting to start but cannot successfully light or detect a steady flame, so it has shut down for safety.

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

Ignition, pilot or flame proving fault

What causes this fault?

This fault occurs when the boiler cannot establish a stable flame to begin the heating process after several attempts. It is usually caused by a blocked pilot light injector, a faulty electronic ignition component, or a gas valve that is failing to release gas to the burner.

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

Neon 1View →Neon 2View →Neon 3View →

Related guides you might find useful

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

Pilot light keeps going out

Older boilers — thermocouple, draught, gas supply.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →