Boiler displays A03 and will not start, fan does not run or runs briefly then stops
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.
Possible Causes
How to Fix / Troubleshooting
Safety: A flue gas fault can indicate risk of carbon monoxide. Turn off the boiler and ventilate the room. Do not operate the boiler until the fault is investigated.
Homeowner checks:
- Go outside and inspect the flue terminal for obstructions (ice, snow, nests, leaves). Remove any visible blockage without damaging the terminal.
- Check the condensate pipe outside for freezing or blockage. If frozen, thaw gently with warm (not boiling) water and lag the pipe.
Technician checks:
- Inspect the entire flue system for correct assembly, slope, and integrity according to IVT installation instructions.
- Check and clean the condensate trap and siphon inside the boiler.
- Test the flue gas temperature sensor (NTC) resistance and wiring; replace if out of specification.
- Verify fan operation and speed feedback to the PCB. Replace the fan assembly if it fails to reach commanded speed.
Do not bypass or bridge any flue safety devices.
Repair Difficulty
Required Part
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