Set Appliance State:

Mains Power Off
Selector switch to DHW position
DHW Preheat selector to MAX position
Ensure appliance is cool and that there is a demand for preheat
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

With preheat demand does the pump run?
Do not take sound or vibration as an indication of the pump running.