Set Appliance State:

Mains Power Off
Use Insulation Mat as required
Set Multimeter to AC Volts Set meter to measure AC Volts
DHW to ON at programmer
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage between White wire (second connector from top) and Neutral (bottom connector) of X15.
Mains voltage expected.