Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
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:

Test 1.
With No DHW demand present measure for DC voltage between pin 11 (black) and pin 12 (black) on connector CN31.
Expected voltage approx. 5 VDC.
Test 2.
Turn hot water tap ON with a flow rate of 3 l/min, repeat voltage measurement as per test 1.
Expected voltage approx. 0 VDC.