Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
DHW Demand
Gain access to PCB (use insulation mat as necessary)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Approximately 5-10 seconds after power is restored to the appliance mains voltage should be present between pin 3 (blue) and pin 4(brown) of connector X3 at the main PCB.