What does the Baxi Duo-tec F91 fault code mean?
The F91 fault code on a Baxi Duo-tec boiler indicates a domestic hot water (DHW) operational fault, which means the boiler is unable to provide hot water as expected. This can lead to issues with water temperature regulation or complete lack of hot water supply.
Common Causes
- Blocked DHW Heat Exchanger: A blockage in the heat exchanger can prevent hot water from being delivered effectively.
- Faulty DHW Sensor: A malfunctioning sensor may not accurately detect the water temperature, leading to operational faults.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer for any repairs related to gas or electrical components. However, you can check the pressure gauge and ensure it is within the normal range (1-1.5 bar) and reset the boiler if necessary.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for addressing the F91 fault could range from £150 to £300, depending on whether the issue is a blocked heat exchanger or a faulty sensor. Costs include parts and labour for a qualified engineer.