What does the Glow-worm Ultimate F91 fault code mean?
The F91 fault code on the Glow-worm Ultimate indicates a Domestic Hot Water (DHW) temperature alert, suggesting that the water temperature is either too high or too low. This alert is a safety feature designed to prevent scalding or damage to the boiler.
Common Causes
- Faulty DHW Temperature Sensor: A malfunctioning sensor may provide incorrect readings, triggering the alert.
- Blocked Heat Exchanger: A blockage can prevent proper heat transfer, leading to temperature inconsistencies.
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 to fix it yourself could pose safety risks.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for addressing the F91 fault could be around £150 to £250, primarily for replacing the DHW temperature sensor or cleaning the heat exchanger, depending on the specific issue identified by the engineer.