Interlocks and permissives in a heat pump: what must be active before startup

Before compressor operation is allowed, the controller checks a series of conditions to ensure the unit starts safely.

Water flow

There must be sufficient circulation in the hydraulic circuit.

Water pressure

The system pressure must be within the permissible limits.

Sensors

Critical temperature and pressure sensors must provide valid readings.

Communications

If there are inverters, indoor/outdoor boards, or BMS interfaces, there must be proper communication.

Safety chain

Any active safety interlock can prevent startup until the cause is resolved.