B4
Nibe
Supply fan fault
B4 alarm, fan not running, no airflow through furnace/air module
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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
Failed fan motor, blocked fan wheel, faulty fan speed controller, wiring fault
How to Fix / Troubleshooting
Safety: Disconnect power before accessing the fan. Moving parts and sharp edges present.
- Check air filters: Severely clogged filters can overload the fan. Replace or clean Nibe‑specified filters.
- Inspect fan wheel: Remove the access panel and check for debris or ice obstructing the fan. Clear obstructions carefully.
- Test fan spin: With power off, spin the fan wheel by hand. It should rotate freely without scraping.
- Check connectors: Ensure the fan motor plug and any speed control connectors are firmly seated.
If the B4 alarm persists and the fan does not start, the fan motor or control board likely needs replacement by a technician.
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Repair Difficulty
Hard
4/5
Required Part
Supply Fan Motor
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