Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach temperature clamps to flow and return pipes as shown in the picture
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance to skip self check and allow boiler to run for DHW demand.
After approx. 2 minutes the temperature should differential should be 20°C or less.