What does the Vaillant ecoTEC plus F91 fault code mean?
The F91 fault code on the Vaillant ecoTEC plus indicates a problem with the system’s training, which typically relates to issues with the boiler’s control system or its ability to adapt to the heating requirements of the home.
Common Causes
- Control Board Malfunction: A failure in the control board can prevent the boiler from properly learning and adjusting to the heating demands.
- Sensor Issues: Faulty temperature or pressure sensors may provide incorrect readings, leading to improper system training.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer for this issue, as it involves the boiler’s control system and may require specialized knowledge and tools to diagnose and repair safely.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for resolving the F91 fault could be around £150 to £300, depending on whether the control board needs replacement or if sensors require recalibration or replacement.