Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach temperature clamps to the flow and return pipes as indicated by the red arrows ensuring a good contact
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to operate for hot water for 2 - 3 minutes.
Measure the temperature differential.
Expected temperature differential approximately 20°C or less.