Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Voltage Set meter to measure AC Volts
Turn Hot Water Tap On
Use Insulation Mat as required
Selector switch to hot water
DHW temperature selector to maximum
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage across the brown and blue wires at connector J3 on the main PCB.