Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn hot water tap on fully
Attach temperature clamps to flow and 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 run in DHW mode for a few minutes.
Monitor the temperature differential as the appliance runs in DHW mode.
Expect a temperature differential of approximately 25°C or less.
Is the temperature differential as expected?