The circulator does not start: electrical and hydraulic diagnosis

If the circulator does not start, the heat pump will usually trigger a low flow or other related alarm.

Is there a command?

Check if the controller is actually sending a command to the circulator.

Is there power supply?

Check the fuse, relay, voltage, and electrical connections.

Mechanical blockage

After a long period of inactivity, the rotor may have seized.

EC/PWM models

For electronic circulators, also check the control signal and any fault codes from the pump itself.