Midea Heat pump fault PB

What it means

Protects the water side heat exchanger from ice formation, controlled based on outdoor ambient temperature, water inlet temperature and water outlet temperature. In cooling mode, triggered if inlet, leaving, or auxiliary heat source leaving water temperature is below 4°C. In heating/DHW mode, triggered if ambient temperature is below 3°C and inlet/leaving/auxiliary heat source leaving water temperature is below 4°C, or if leaving water temperature is below 2°C.

Likely causes

1. Low water flow
2. Flow switch leak due to faulty sealing ring
3. External pump starts before internal pump (PUMPI) starts
4. The water flow in the pipe is not consistent with arrow on the flow switch
5. Flow switch FS plug (CN8) is not connected properly
6. Water flow switch rake mechanically damaged
7. Flow switch not installed properly
8. Water flow switch mechanically damaged (rake does not trigger contact closure)
9. Pump stalling due to impeller obstruction
10. Water pump internal failure despite correct wiring
11. Water pump malfunction indicated by abnormal indicator light status
12. Water pump leak due to faulty sealing ring
13. Water pump connection is correct, the water pump icon on the User Interface is lit, while no indicator lights on water pump is lit
14. Pump idling
15. Pump idling due to insufficient water/air in circuit

Where to start

1. Check water flow rate and pump operation
2. Monitor Min(Twout,Twin,T1) against 15°C threshold for heat pump stop condition
3. Inspect flow switch for leaks