High Lockout
Neon3 on Ideal Classic FF

Your boiler has lost power to its main control board, meaning it cannot operate and you will not have any heating or hot water.

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

Main supply to PCB 25B.

What causes this fault?

This fault occurs when the boiler's internal computer stops receiving the steady stream of electricity it needs to function. It is usually caused by a component failure on the control board itself, a blown internal fuse, or a faulty transformer that can no longer convert power correctly. Essentially, the 'brain' of the boiler has lost its power supply and can no longer tell the other parts to turn on.

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 →

Related guides you might find useful

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

No hot water but heating works

Almost always a stuck diverter valve on combis.

Read →

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →