F04
Ferroli
DHW Sensor / Modulation Communication Error
Thermostat shows F04 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
Faulty DHW NTC sensor in boiler not reporting correctly to thermostat, BUS communication error specific to DHW channel, Incorrect configuration of DHW control in thermostat menu, Firmware bug in thermostat DHW control module
How to Fix / Troubleshooting
Safety first: DHW sensors are inside the boiler. Do not open the boiler casing unless qualified. You may adjust only thermostat settings.
- Check DHW settings:
- Enter the Ferroli thermostat menu and verify that DHW control is enabled if your boiler supports it.
- Ensure the DHW setpoint is within the allowed range.
- Reset BUS communication:
- Power cycle the boiler and thermostat receiver.
- After restart, check if F04 clears and if DHW temperature can be adjusted.
- Test DHW at boiler:
- Try adjusting DHW temperature directly on the boiler front panel (if available).
- If the boiler also fails to regulate DHW, the issue is likely the boiler's DHW NTC or PCB.
- Call a technician if unresolved:
- Report that the Ferroli smart thermostat shows F04 and cannot modulate DHW; a technician should test the boiler's DHW NTC sensor and BUS interface.
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Repair Difficulty
Hard
4/5
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