Set Appliance State:

Mains Power Off
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
DHW Selector in Minimum (-) position
CH Selector in Maximum (+) position
ON/OFF Switch in ON position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

On the 24 hr clock, to the left side of the Control box, measure the voltage across the right of the two red leads and the blue lead (neutral).
Expect mains voltage.