Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
Selector switch set to DHW
Preheat switched OFF
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure for DC voltage across pin 10 (X8 connector PCB) and main neutral (terminal block).
Expected voltage approximately 5 Vdc.