What does the Glow-worm Ultimate F78 fault code mean?
The F78 fault code on the Glow-worm Ultimate indicates a problem 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 supply.
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 disrupt its function, causing the fault code to appear.
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 cost for repairing the F78 fault, including replacing the DHW thermistor, is around £120-£150. This includes parts and labour, as the thermistor itself typically costs about £30-£50.