What does the Viessmann Vitodens 111-W F90 fault code mean?
The F90 fault code on the Viessmann Vitodens 111-W indicates a problem with the domestic hot water (DHW) maintenance system. This typically suggests that the boiler is unable to maintain the required temperature or pressure for hot water production.
Common Causes
- Faulty DHW Sensor: A malfunctioning sensor can lead to incorrect temperature readings, causing the system to fail in maintaining hot water.
- Blocked Heat Exchanger: A blockage in the heat exchanger can restrict water flow, preventing the boiler from heating water effectively.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer for this issue, as it involves gas and electrical components that require professional handling. Attempting DIY repairs could be dangerous.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for addressing the F90 fault could range from £150 to £300, depending on whether the DHW sensor needs replacement or if the heat exchanger requires cleaning or servicing.