BoilerFaultCodesViessmann 9C:0 Fault Code
Also written as 9C0 — same fault.
The Viessmann 9C:0 fault code means: your boiler has stopped working because its internal control computer has lost its configuration settings or is unable to communicate with its safety sensors.. It appears on 5 Viessmann models in our database.
Technical description: No monitoring
What causes the Viessmann 9C:0 fault?
This fault occurs when the boiler's main control unit loses the specific digital 'identity' required to operate your heating system safely. It is typically caused by a corrupted coding chip or a breakdown in communication between the central computer and the internal sensors. Without these settings, the boiler shuts down as a safety precaution because it no longer knows its own technical parameters.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Viessmann models that show the 9C:0 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 9C: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