Set Appliance State:

Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
CH temperature selector to 0 position
DHW temperature selector to 0 position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Allow appliance to self check and return to standby mode.
DHW temperature selector to maximum position.
Does the fan run at high speed while the burner is a light or does the fan slow down before burner shuts down?