BoilerFaultCodesViessmann 80:0 Fault Code
Also written as 800 — same fault.
The Viessmann 80:0 fault code means: your boiler is experiencing a communication error between its control system and the temperature sensors, meaning it cannot accurately monitor the water temperature.. It appears on 5 Viessmann models in our database.
Technical description: Without time delay
What causes the Viessmann 80:0 fault?
This fault occurs when the boiler's central brain loses contact with the sensors that monitor heat levels, often due to a broken internal wire or a sensor that has failed completely. Because the control system can no longer safely tell how hot the water is, it shuts down to prevent the system from overheating. It is usually caused by a physical break in the electrical circuit or moisture damage to the sensitive electronic connections.
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 80:0 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 80:0 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