BoilerFaultCodesViessmann b7 Fault Code
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 5 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.
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.
- Viessmann Vitodens 100-W manual (PDF)
- Viessmann Vitodens 222-F manual (PDF)
- Viessmann Vitodens 242-F B2UA manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026