What does the Glow-worm Ultimate F40 fault code mean?
The F40 fault code on the Glow-worm Ultimate indicates a domestic hot water (DHW) flow fault, which typically means that the boiler is unable to detect or maintain the required flow of hot water. This can lead to insufficient hot water supply for taps and showers.
Common Causes
- Blocked DHW Flow Sensor: A blockage in the flow sensor can prevent accurate readings, leading to the F40 fault code.
- Faulty Diverter Valve: If the diverter valve is stuck or malfunctioning, it may not direct water flow correctly, causing the boiler to register a fault.
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 can be dangerous to handle without proper training. Attempting to fix it yourself may void any warranties and could pose safety risks.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for resolving an F40 fault could range from £150 to £300, depending on whether the issue is a simple sensor replacement or a more complex diverter valve repair. This estimate includes parts and labour for a qualified engineer.