Set Appliance State:

Mains Power Off
Set Multimeter to AC Volts Set meter to measure AC Volts
Operating Switch in the Heating & Water position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure Mains voltage across connector X11 connection 1 (L) and Terminal block X4 connection 2 (N).
Measure Mains voltage across connector X11 connection 2 (L) and Terminal block X4 connection 2 (N).