What does the Glow-worm Ultimate F90 fault code mean?
The F90 fault code indicates a problem with the domestic hot water (DHW) flow switch, which may be stuck or malfunctioning. This prevents the boiler from detecting water flow, leading to a failure in providing hot water.
Common Causes
- Blocked Flow Switch: Debris or mineral build-up can obstruct the flow switch, preventing it from operating correctly.
- Electrical Fault: Issues with wiring or connections to the flow switch can cause it to fail to send the correct signals to the boiler.
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 expertise. Attempting repairs without proper training can be dangerous.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for a faulty flow switch on a Glow-worm Ultimate boiler is around £150 to £200. This includes the cost of the replacement part and labour, as flow switches are relatively inexpensive but require professional installation.