F5
Saunier Duval
DHW Control Communication Error
Thermostat shows F5 and cannot control domestic hot water temperature via the boiler
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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.
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Possible Causes
Incorrect configuration of DHW control in thermostat settings, Boiler DHW sensor or board not responding on bus, Incompatible boiler model for smart DHW control, Faulty eBus/OTBus connection for DHW data
How to Fix / Troubleshooting
Safety: Switch off boiler power before opening its front cover.
- Check compatibility: Confirm that your Saunier Duval boiler model supports DHW control via the smart thermostat (consult boiler and thermostat manuals).
- Verify settings: In the thermostat menu, ensure DHW control is enabled and the correct boiler type is selected.
- Inspect bus wiring: Confirm the communication cable is correctly connected to the boiler's bus terminals and not to a simple on/off thermostat input.
- Boiler self-test: On the boiler control panel, adjust DHW temperature directly. If the boiler does not respond or shows its own error, the issue is in the boiler DHW sensor or PCB, not the thermostat.
If F5 remains and the boiler works normally from its own panel, the thermostat or its configuration may be faulty; consider firmware update or replacement.
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Repair Difficulty
Medium
3/5
Required Part
Saunier Duval Smart Thermostat (DHW Control Function)
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