What does the Glow-worm Ultimate F42 fault code mean?
The F42 fault code on the Glow-worm Ultimate boiler indicates a fault with the domestic hot water (DHW) thermistor. This component is responsible for measuring the temperature of the water, and a fault can lead to issues with hot water delivery.
Common Causes
- Faulty DHW Thermistor: The thermistor may be malfunctioning or damaged, leading to incorrect temperature readings.
- Wiring Issues: Damaged or loose wiring connections to the thermistor can cause communication problems with the boiler’s control system.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer for this issue, as working with gas appliances can be dangerous. Attempting to fix electrical components without proper training can lead to further complications.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for replacing the DHW thermistor is around £120, which includes the part and labour. This cost reflects the complexity of the repair and the need for a qualified engineer to ensure safety and compliance.