High Lockout
F20 on Glow-worm Ci Plus

Your boiler's internal computer parts are having trouble communicating with each other or have been replaced with mismatched versions.

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

User interface / Main PCB incompatibility

What causes this fault?

This fault occurs when the boiler's main control board and the display panel are unable to talk to each other correctly. It most commonly happens after a repair where a new part has been installed that isn't compatible with the existing software or model version. In some cases, it can also be caused by a loose connection or a sudden electrical surge that disrupts the internal communication between these two components.

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.

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