Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Unclip the flow switch from its housing and
wedge it above the pressure gauge as shown
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Find a suitable strong magnet. This could be the back of the socket & see as shown, the back of a FGA or a magnetic pen. A magnetic screwdriver is not strong enough to be used for this test.
Move the magnet so that it is directly above the circle in the flow switch (see arrow) for at least 5 seconds.
Does the pump begin to run?
Additional Information:
This type of flow switch operates by detecting a
magnet moving within the housing. This test
mimics the effect.