What does the Glow-worm Ultimate F35 fault code mean?
The F35 fault code indicates a system pressure fault, which typically means that the boiler’s water pressure is either too low or too high. This can prevent the boiler from operating efficiently and may lead to further issues if not addressed promptly.
Common Causes
- Low Water Pressure: This can occur due to leaks in the system, a faulty pressure relief valve, or insufficient water supply.
- High Water Pressure: This may be caused by a malfunctioning pressure reducing valve or an issue with the expansion vessel.
Can I fix it myself? (DIY)
If the issue is low pressure, you can attempt to repressurise the system by using the filling loop, following the manufacturer’s instructions. However, for any gas or electrical issues, it is crucial to call a Gas Safe Engineer to ensure safety and compliance with regulations.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for addressing a pressure fault on a Glow-worm Ultimate boiler is around £150 to £250, depending on whether a part needs replacing, such as a pressure relief valve or expansion vessel, and the labour involved.