What does the Viessmann Vitodens 111-W F99 fault code mean?
The F99 fault code on the Viessmann Vitodens 111-W indicates an issue with the heating circuit firmware. This typically suggests that the boiler’s control system is not functioning correctly, which can affect the heating performance.
Common Causes
- Firmware Corruption: The firmware may have become corrupted due to a power surge or improper updates.
- Software Glitch: A temporary software glitch can cause the control system to malfunction, leading to the F99 error.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer to address this issue, as it involves the boiler’s control system and firmware, which requires professional expertise to diagnose and repair safely.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for addressing the F99 fault code is approximately £150 to £250. This includes the cost of a technician’s visit and potential firmware reprogramming or replacement of the control board if necessary.