Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
Ensure boiler is cool
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance if required.
When the boiler has recognised a DHW demand (tap symbol flashing), does the fan run?
Note:
It may take approximately 40 seconds for the boiler to recognise a demand (tap symbol flashing), this will depend upon the boiler status. (Status code guidance CLICK HERE)