Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to AC Volts 
DHW Demand
Remove control box cover if necessary
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure the voltage between the white wire on connector X13 and the neutral at the incoming mains terminal strip, with the connector X13 attached to the PCB.
Expect mains voltage.
Expect mains voltage.
Isolate as per TOPs P4
and refit as necessary