BoilerFaultCodesViessmann bF Fault Code
Also written as BF — same fault.
The Viessmann bF fault code means: your boiler is having trouble communicating with an internal connection module, which means it cannot properly coordinate its heating and hot water functions.. It appears on 3 Viessmann models in our database.
Technical description: Control mode Incorrect LON communication module
What causes the Viessmann bF fault?
This fault occurs when the boiler’s automated filling system becomes stuck or fails to complete its cycle, often because the system cannot reach the required pressure. The most common reason is a manual filling valve being left open by mistake or a malfunction in the electronic sensor that monitors the water level. In some cases, the internal control board may be unable to register that the filling process has finished, causing the boiler to halt for safety.
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 bF fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann bF fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
- Viessmann Vitodens 050-W manual (PDF)
- Viessmann Vitodens 222-F manual (PDF)
- Viessmann Vitodens 333-F manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026