Set Appliance State:
Use Insulation Mat as required
Set Multimeter to AC Volts 
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Selector switch to WATER
Gain access to PCBs
Selector switch to WATER
Gain access to PCBs
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure voltage between brown wire on connector X21 on sequence board and neutral X4 on main driver board.
Isolate as per TOPs P4
and refit as necessary