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
Selector switch set to ch/dhw
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure for mains voltage across connections brown (live) and blue (neutral) leads at connector marked CN2 on the PCB.
Expect mains voltage.