Set Appliance State:

Turn Hot Water Tap On
Pre-heat switched OFF (turn comfort switch to E position)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to fire and run for DHW demand.
Turn OFF hot water tap, does the boiler end DHW demand straight away or continue to fire?
Note.
This test is to check for a sticking DHW flow switch, as this may occur intermittently repeat test several times until you are satisfied flow switch is functioning correctly.