Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
Ensure selector switch is set to DHW/CH position.
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure for DC voltage across test point 1 & 3.
Expected voltage approximately 4.6 Vdc.
Note.
Ensure a good connection is made as misdiagnosis will occur.