Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Gain access to PCB (use Insulation Mat as required)
Selector switch to DHW position
DHW Preheat selector to MAX position
Ensure a demand for preheat
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage at connection 3 (blue wire) and connection 6 (brown wire) on connector A4
on the main PCB.