High Lockout
06 on Glow-worm EnergySaver Combi

Your boiler's internal computer has encountered a critical error and can no longer control the heating and hot water functions safely.

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

There is an internal fault in the Automatic Control Module.

What causes this fault?

This fault occurs when the boiler's main control board experiences a hardware failure or a memory error, meaning it can no longer process data correctly. The most common reason is natural wear and tear of the electronic components, though electrical surges or moisture getting onto the board can also trigger this complete failure.

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

03View →04View →

Related guides you might find useful

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 →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →