What does the Glow-worm Ultimate F39 fault code mean?
The F39 fault code indicates a fault with the domestic hot water (DHW) sensor in the Glow-worm Ultimate boiler. This issue can prevent the boiler from properly heating water for taps and showers.
Common Causes
- DHW Sensor Failure: The sensor may be malfunctioning or damaged, leading to inaccurate temperature readings.
- Wiring Issues: Damaged or loose wiring connections to the DHW sensor can disrupt communication between the sensor and the boiler’s control board.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer for this issue, as it involves electrical components and gas safety regulations. Attempting to fix it yourself could pose safety risks.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for replacing the DHW sensor is around £150 to £200, including parts and labour. This cost reflects the price of the sensor and the expertise required for safe installation.