High
b1 on Viessmann Vitodens 300-W

Your boiler's main control panel is having trouble talking to the internal computer, meaning you cannot adjust settings or operate the unit 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

Control mode: Communication fault – programming unit (internal)

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

b0View →b5View →b7View →

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