How much does it cost to fix Viessmann error code b7?

Typical repair cost for the Viessmann b7 fault is £120-350 including labour.

b7 High

Viessmann b7 Fault Code

Q: What does the Viessmann b7 fault code mean?

Your boiler's internal computer chip has been disconnected or has developed a communication fault, meaning the system doesn't know which settings to use.

Also written as B7 — same fault.

The Viessmann b7 fault code means: your boiler's internal computer chip has been disconnected or has developed a communication fault, meaning the system doesn't know which settings to use.. It appears on 8 Viessmann models in our database.

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

What causes the Viessmann b7 fault?

This fault occurs when the boiler's main control board loses communication with the small plug-in memory chip that stores the unit's identity and settings. The most common reason is that the chip has vibrated loose, suffered from a hardware failure, or the main circuit board itself can no longer read the data due to a technical glitch.

Typical repair cost £120-350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Viessmann models that show the b7 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Viessmann b7 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026