Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
Gain access to PCB (use Insulation Mat as required)
Selector switch to DHW and CH position
DHW temperature selector to maximum
CH temperature selector to minimum
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage at connection 3 (blue wire to the right of the red wire) and connection 6 (1st brown wire on the right) on connector A4 on the main PCB.