Set Appliance State:

Mains Power Off
Set Multimeter to AC Volts Set meter to measure AC Volts
DHW Demand
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the AC voltage between the Switched Live (marked L2) and Neutral (marked N) at the incoming side of the connector block.
Expect Mains voltage