Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
Turn hot water tap on with a flow rate of 3 l/min
Ensure the selector switch is in heating and hot water mode
DHW temperature selector to MAX
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Observe the lights on the front of the boiler, with the tap running does the Hot Water Demand light (tap symbol) show?
Turn hot water tap OFF.
Does the hot water demand light now turn off?
Note:
It is advisable to repeat this test several times as the flow switch may stick or not make intermittently.