F17
Ferroli
Modulation Control Fault / Stuck Demand Signal
Thermostat shows F17 and the boiler runs at maximum temperature regardless of setpoint.
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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
Shorted BUS control line causing constant maximum demand, Firmware bug in modulation algorithm, Incorrect boiler type or maximum output configured, Faulty DAC/output stage on thermostat PCB
How to Fix / Troubleshooting
Safety first: Overheating radiators can be dangerous. Monitor system temperature and do not cover radiators.
- Check thermostat settings:
- Verify maximum flow temperature and heating curve settings in the installer menu.
- Disable advanced modulation and test in simple on/off mode if available.
- Inspect BUS wiring:
- Isolate power and check BUS cable for shorts between conductors.
- Test boiler in standalone mode:
- Disconnect BUS and, if possible, run boiler using its own controls or a simple on/off link.
- If boiler modulates correctly without the thermostat, the thermostat is at fault.
- Replace thermostat if needed:
- If F17 persists and boiler behaves normally without BUS, replace the Ferroli smart thermostat.
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Repair Difficulty
Hard
4/5
Required Part
Ferroli Smart Thermostat (Modulation Output Stage)
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