Set Appliance State:

Mains Power Off
Set Multimeter to AC Voltage Set meter to measure AC Volts
Turn Hot Water Tap On
Selector switch to DHW and CH position
CH temperature selector to Max
DHW temperature selector to Min
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage at connection 5 (brown wire) and connection 4 (blue wire) on connector X3 on the main PCB.