Heat pump fails to start: organized check from basic to complex

When a heat pump fails to start, proper diagnosis should be performed in a systematic order rather than through random setting changes.

Power supply check

Verify that there is a proper electrical supply, that the fuses are active, and that there is no general electrical fault.

Check if there is an actual heating or cooling demand from the thermostat, BMS, or controller.

Flow switch, water pressure, sensors, and other permissives may be preventing startup.

The last fault code and the chronological sequence of events are often more useful than a simple reset.