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:

After approximately 13 seconds voltage should be present at test points.
Measure the voltage across the purple leads on connector 4 on the PCB.