BoilerFaultCodesViessmann b0 Fault Code
Also written as B0 — same fault.
The Viessmann b0 fault code means: your boiler has stopped working because it has detected a technical fault with the sensor that monitors the heat of the exhaust gases.. It appears on 9 Viessmann models in our database.
Technical description: Burner blocked - Flue gas temperature sensor short circuit
What causes the Viessmann b0 fault?
This fault occurs when the boiler's internal computer receives an incorrect electrical signal from the sensor that monitors the temperature of the exhaust fumes. The most common reason is that the sensor itself has suffered an internal failure or the electrical wiring connecting it to the main control board has become damaged or loose. Because the boiler can no longer safely monitor how hot the waste gases are, it shuts down immediately as a safety precaution.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Viessmann models that show the b0 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann b0 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