What does the Viessmann Vitodens 100-W F85 fault code mean?
The F85 fault code on the Viessmann Vitodens 100-W indicates a faulty phase, which typically relates to an issue with the electrical supply or phase connection to the boiler. This can prevent the boiler from operating correctly, leading to heating and hot water issues.
Common Causes
- Electrical Supply Issue: A disruption or fault in the electrical supply can cause the boiler to register a faulty phase.
- Wiring Fault: Damaged or loose wiring connections within the boiler can lead to incorrect phase detection.
Can I fix it myself? (DIY)
It is strongly advised to call a Gas Safe Engineer for this issue, as it involves electrical components that can be dangerous if handled improperly. Attempting to fix electrical faults without proper training can pose serious risks.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for resolving the F85 fault could range from £150 to £300, depending on whether it requires a simple wiring fix or replacement of electrical components. This estimate includes labour and parts, reflecting the complexity of electrical repairs.