Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Run hot water tap at flow rate of 3 l/min
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage between the brown at connector X13 and the neutral at the incoming mains terminal strip, with connector X13 attached to the PCB.
Expect mains voltage.