What does the Glow-worm Ultimate F99 fault code mean?
The F99 fault code on the Glow-worm Ultimate indicates a warning related to the domestic hot water (DHW) flow switch. This typically suggests that the flow switch is either malfunctioning or not detecting water flow correctly, which can affect the boiler’s ability to provide hot water.
Common Causes
- Faulty Flow Switch: The flow switch may be defective or worn out, preventing it from accurately detecting water flow.
- Blocked Water Path: A blockage in the water supply or within the boiler can restrict flow, causing the flow switch to trigger a fault.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer to diagnose and repair this issue, as it involves gas and electrical components that require professional expertise.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for fixing the F99 fault code is around £150 to £250, primarily due to the potential need for a new flow switch and the labour involved in diagnosing and resolving the issue.