BoilerFaultCodesViessmann C7 Fault Code
The Viessmann C7 fault code means: your boiler is having trouble communicating with the internal pump that moves hot water through your radiators, which may prevent your heating from working correctly.. It appears on 8 Viessmann models in our database.
Technical description: Control mode, max. pump speed - Communication fault-variable speed heating circuit pump, heating circuit A1
What causes the Viessmann C7 fault?
This fault occurs when the boiler's main control board loses its electronic connection with the internal circulation pump. It is usually caused by a loose or damaged wiring connection between these two parts, or a total failure of the pump's internal electronics. Without this communication, the boiler cannot adjust the flow of water around your home and will stop heating for safety.
This fault often appears at the start of autumn when the heating is turned on for the first time after summer, as pump components can seize or struggle after long periods of inactivity.
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 C7 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann C7 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