BoilerFaultCodesViessmann 0C Fault Code
The Viessmann 0C fault code means: your boiler has shut down because the electrical power coming into it is too weak or unstable to run safely.. It appears on 7 Viessmann models in our database.
Technical description: Burner fault. Mains voltage is too low. Check the power supply.
What causes the Viessmann 0C fault?
This fault occurs when the boiler's internal computer detects that the incoming electricity supply has dropped below a safe working level. The most common reason is a problem with your home's electrical circuit or a failing component on the boiler's main control board that can no longer process power correctly.
This issue can occasionally trigger during peak winter months if the local electrical grid is under heavy strain or during stormy weather that causes fluctuations in power stability.
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 0C fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 0C 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