Set Appliance State:
Mains Power Off
Set Multimeter to AC Volts 
Turn Hot Water Tap On
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure for mains voltage between the grey wire (pin 4) on X20 on the sequence board and neutral on X4 on the main driver board.
Isolate as per TOPs P4
and refit as necessary