Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach temperature probes/clamps to the flow & return pipes
(as indicated by the red arrows)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the appliance to operate for hot water for 2 - 3 minutes.
Monitor the temperature differential across the flow and return pipes.
Expected temperature differential approximately 22°C or less.