Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
CH Demand
Disconnect the fan connector from the fan assembly
(place in a safe position)
On-Off switch on
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the dc voltage between connector x20, connection 4 (grey) and a suitable earth.
Expected voltage approx. 24vdc.

Note:
Voltage will be present after approx. 10 seconds after the pump starts.