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:

Measure the voltage between pin 6 (violet)
at CN9 to a suitable earth point.
Voltage should be approximately 2.7V DC.
Note:
At lower flow rates voltage may fluctuate slightly.