High
b7 on Viessmann Vitodens 300-W

Your boiler's internal computer chip is either missing, faulty, or not communicating correctly with the main controls, meaning the unit cannot start for safety reasons.

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

Burner blocked: Boiler coding card missing, faulty or incorrect card inserted

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 →b8View →

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