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
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:

Reset appliance if required (Press reset button once then release)
Allow fan to run.
Measure the DC voltage between pin 3 on connector X2 and a suitable earth point.
Expect approximately 4.5vdc.