Set Appliance State:
Mode selector switch to Off/Reset position
Set Multimeter to AC Volts 
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Hot water temperature control set to maximum
Gain access to PCB (use insulation mat as necessary)
Hot water temperature control set to maximum
Gain access to PCB (use insulation mat as necessary)
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Mode selector switch to DHW position.
Measure the voltage across live (brown wire) on connector M12 on the main PCB and a suitable neutral.
Measure the voltage across live (brown wire) on connector M12 on the main PCB and a suitable neutral.
Isolate as per TOPs P4
and refit as necessary