Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
DHW Demand
Gain access to PCB (use Insulation Mat as required)
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage across connection 2 (red lead)
and connection 3 (black lead) on connector X22.
Expected voltage greater than 23 volts DC.