Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC 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 DC volts between blue on the connector X23 and the neutral at the incoming mains terminal strip, with the connector X23 attached to the PCB.
Expect between 5-20 vdc.
Expect between 5-20 vdc.
Isolate as per TOPs P4
and refit as necessary