Boiler displays F6 and will not fire for central heating or hot water
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Safety first: Isolate electrical power and water supply to the boiler before removing covers or sensors.
Steps to check:
- Locate the DHW NTC sensor on or near the domestic hot water plate heat exchanger.
- Inspect the sensor body and wiring for signs of water ingress or damage.
- Disconnect and measure the sensor resistance at room temperature; compare with Saunier Duval specifications.
- Replace the DHW NTC if readings are incorrect or intermittent.
- If hot water temperature has been unstable, consider descaling or replacing the plate heat exchanger, as heavy scale can cause sensor errors.
Warning: DHW components are under mains water pressure. Ensure the water is isolated and pressure relieved before removing any parts.
Repair Difficulty
Required Part
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