Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to AC Volts 
Gain access to PCB (use Insulation Mat as required)
Selector switch to DHW position
Selector switch to DHW position
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure voltage across the Brown wire (live) and the Blue wire (neutral) on the boilers main terminal strip.
Expect mains voltage.
Expect mains voltage.
Isolate as per TOPs P4
and refit as necessary