A03
Ferroli Flue / Safety Device Trip Feedback

Thermostat shows A03 and heating is disabled; boiler indicates flue or safety sensor trip.

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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

Blocked flue or terminal, Faulty flue gas sensor in boiler, Overheating of flue components, Incorrect boiler installation or ventilation issue

How to Fix / Troubleshooting

Critical safety warning: A03 may indicate a flue or combustion safety problem. Do not attempt to access the boiler combustion chamber or flue. Risk of carbon monoxide exposure.

  • Visual external checks only:
    • Ensure the outside flue terminal is not blocked by debris, snow, or vegetation.
    • Check that air vents around the boiler are not obstructed.
  • Reset sequence:
    • Turn off the boiler and thermostat for 1 minute.
    • Restore power and see if A03 clears.
  • If A03 returns:
    • Do not continue to reset and run the boiler.
    • Contact a qualified Ferroli service technician immediately and report the A03 flue/safety trip.
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Repair Difficulty

Professional Required 5/5
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