Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach temperature probes as indicated by the red arrows
(PCB housing may need to be removed from holder to gain access)
DHW thermostat set to MAX
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Measure the temperature differential.
Expect approximately 22°C or less.