Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
DHW temperature set to MAX
DHW flow rate NO greater than 9.8 litres/min
Attach temperature clamps to flow and return
pipes of the primary heat exchanger
Note:
Ensure a good connection is made with the flow & return pipes
or mis-diagnosis will occur
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow appliance to operate for hot water for 3 minutes.
Monitor the temperature differential across flow and return pipes.
Expected temperature differential approximately 20°C or less.