BoilerFaultCodesViessmann FC Fault Code
The Viessmann FC fault code means: your boiler has detected a failure in its internal gas control system, meaning it cannot safely start the burner to heat your home or water.. It appears on 7 Viessmann models in our database.
Technical description: Burner in fault position. Modulation coil faulty. Check the gas train.
What causes the Viessmann FC fault?
This fault occurs when the boiler's control system loses the ability to precisely adjust the amount of gas entering the burner. The most common cause is a failure in the electrical coil that moves the internal gas valve, meaning the boiler can no longer maintain a safe and steady flame to heat your home.
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 FC fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann FC 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