Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
Selector Switch to ch/dhw
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure for mains voltage across connections 1(brown) and 2 (blue) on connector CN4 at the PCB.
Note:
Ensure a good connection is made.