A04
Hoval
Fan / Air Pressure Fault
Boiler displays A04 and will not start, fan does not run
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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
Defective flue fan, Blocked flue or air intake, Faulty air pressure switch or differential pressure sensor, Wiring fault between fan and control board
How to Fix / Troubleshooting
Safety: Isolate electrical power before removing the boiler front panel. Flue work must comply with local regulations.
- Check flue terminal: From outside, ensure the Hoval boiler flue terminal is not obstructed by ice, nests, or debris. Clear any blockage carefully.
- Inspect fan area: Remove the boiler casing and visually inspect the fan for signs of overheating, seized bearings, or foreign objects.
- Spin test: With power off, gently rotate the fan impeller by hand. It should move freely without grinding noises. If seized, the fan must be replaced.
- Pressure switch / sensor tubing: Check silicone tubes from the fan or flue connection to the air pressure switch or differential pressure sensor for splits, kinks, or water ingress. Replace damaged tubing and drain any condensate.
- If the fan does not run even though it is free to turn, a technician should test the fan supply voltage from the main PCB and replace the fan or PCB as required.
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Repair Difficulty
Hard
4/5
Required Part
Flue Fan Assembly
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