High Lockout
CF on Viessmann Vitodens 333

Your boiler's internal communication system has failed, meaning the different electronic parts are no longer talking to each other correctly.

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

Communications fault - LON communication module. Control mode

What causes this fault?

This fault occurs when the main control board loses its connection with the internal plug-in communication module. The most common reason is an electronic component failure within the module itself or a loose physical connection caused by vibrations over time. Without this link, the boiler's brain cannot send or receive the data it needs to operate safely, causing it to stop running.

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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Related fault codes

BCView →BDView →B0View →

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