F05
Ferroli
Power Supply / Low Voltage Fault
Thermostat displays F05 and the screen backlight flickers or unit reboots randomly.
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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
Undersized or faulty 230 V to 24 V transformer feeding thermostat receiver, Loose power terminals on Ferroli receiver, Overloaded receiver relay contacts causing brown‑outs, Internal power regulator fault on thermostat PCB
How to Fix / Troubleshooting
Safety first: The receiver is connected to mains voltage. If you are not competent with 230 V wiring, do not open the receiver. Isolate power at the breaker before removing the cover.
- Check power source:
- Confirm the receiver is connected to a stable mains supply (not via a loose plug or extension).
- Inspect the fuse or breaker feeding the boiler/receiver circuit.
- Inspect terminals (qualified persons only):
- With power isolated, remove the receiver cover.
- Check that the live, neutral, and earth connections are tight and correctly placed.
- Look for signs of overheating or discoloration on the PCB.
- Reduce load on receiver relay:
- Ensure the receiver relay is only switching the boiler control circuit, not additional pumps or loads beyond its rating.
- If F05 continues:
- The internal power supply of the thermostat/receiver may be failing.
- Replace the Ferroli smart thermostat receiver or have it serviced.
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Repair Difficulty
Hard
4/5
Required Part
Ferroli Smart Thermostat Receiver Power Board
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