Set Appliance State:

Set Multimeter to DC Volts Set meter to measure DC Volts
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
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 DC voltage across Yellow connections on connector X2 (Modureg).
Expected voltage at maximum approximately 20vdc