Safety: Isolate electrical power and allow the system to cool before touching the pump or pipework.

1. Listen and feel: On a heat demand, the pump should hum and vibrate slightly. If silent, suspect electrical failure; if humming but not circulating, suspect seizure or air lock.
2. Bleed pump: If the pump has a bleed/vent screw, carefully open it to release trapped air until water appears. Tighten securely.
3. Free the rotor: With power off, remove the vent screw and gently turn the pump shaft with a screwdriver to free it. Replace the screw and test.
4. Check wiring: Ensure the pump connector is secure and that there is no visible damage to the cable.
5. Replace pump or capacitor: If the pump does not start even with correct voltage, replace the ACV primary circulation pump or its start capacitor (if external).

Pump replacement involves draining part of the system and should be done by a heating professional.

Display shows E17, unit may shut down when pump should be running

Possible Causes