Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
Turn Hot Water Tap On
On/Off Switch in ON position
Mode Selector Switch to Summer
DHW Thermostat to MAX
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure Voltage across connection 30 (+ve Red)
and connection 10 (-ve Grey).