Set Appliance State:

Mains Power Off
Mode selector switch to Off/Reset position
Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap ON
Hot water temperature control set to maximum
WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Mode selector switch to DHW position.
Measure the voltage across live (brown wire) on connector M12 on the main PCB and a suitable neutral.