Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Remove the cover from the pump
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

While the external controls are calling for heat check the voltage at the terminals of the pump.
Expect mains voltage.
NOTE:
The pump is external to the boiler.
If you are unsure as to its location ask the customer for help in finding it.