Set Appliance State:

Mains Power Off
Turn Hot Water Tap ON
DHW Temperature Control to MAX
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance (press and hold the reset button for 5 seconds, then release).
Observe how long it takes for the fault code, volatile
lockout to be displayed after appliance reset.
Does the fan run before the appliance returns to lockout?
Note.
If a fault code other than volatile lockout is displayed CLICK HERE