Set Appliance State:

Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Remove control box cover to expose the control PCB
Use insulation mat as necessary
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Reset lockout as necessary.
Measure voltage across connection 2 (blue wire) and connection 4 (brown wire) at connector marked CON 11 on the control PCB.