B5 alarm, reversing valve not operating, no change between heating and cooling (for reversible Nibe units)
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: Refrigerant components must not be opened by unqualified persons. High pressure risk.
- Listen for valve operation: When switching between heating and cooling, you should hear a click from the reversing valve coil. If not, check the coil wiring and connector.
- Measure coil resistance: With power off, a technician can measure the solenoid coil resistance to confirm if it is open circuit.
- Check control signals: Ensure the Nibe controller is actually commanding a mode change (check operating mode in the menu).
A stuck valve or internal refrigerant contamination requires a certified Nibe technician to replace the reversing valve and possibly flush the system.
Repair Difficulty
Required Part
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