Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach a temperature clamp to the flow pipe
(On the pipe near the temperature probe with the red leads)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the burner to ignite and establish (indicated by the blue LED illuminating on the facia).
Monitor the temperature shown on the FGA, the appliance should run to its maximum temperature of approximately 80°C and then either shut down (Blue LED on facia goes out) or modulate to maintain temperature.
Does the appliance behave as described above?
Note.
To speed up this test it may be possible to turn off some radiators temporarily to reduce heat up time.