Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
Turn hot water tap ON with a flow rate of 3 l/min
Move connector CN8 until PCB connection strips are exposed but connector is still in contact with the PCB
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the DC voltage between pin 2 (black) and pin 3 (grey) on the exposed strips on connector CN8 on the PCB.
Expect between 3.6 and 4.4 VDC.
Note:
The voltage may flicker on the multimeter display which is normal at a low flow rate, increasing the flow rate slightly will help stabilise the reading if desired.