High Lockout
F13 on Glow-worm Xtramax HE

Your boiler's main control board has encountered an internal electronic error, meaning the 'brain' of the system can no longer manage the heating and hot water 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

Main PCB fault.

What causes this fault?

This fault occurs when the boiler's internal computer experiences a critical electronic failure or a 'brain freeze' that prevents it from processing commands. It is typically caused by a short circuit on the control board, aged components failing over time, or a communication error between the board and the wiring harness.

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 →F11View →

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 →