Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Unclip the flow switch from its housing and use its hook to wedge it onto the boiler chassis in the bottom left corner as shown
(it may be fitted facing into the boiler if there is insufficient space)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Hold the tip of a magnetic pen or screwdriver next to
the flow switch as shown for at least 5 seconds.
Does the pump begin to run?
If the pump still does not run, place the magnetic pen
or screwdriver on the inside of the flow switch and
observe if the pump then begins to run.
Additional Information:
This type of flow switch operates by detecting a
magnet moving within the housing. This test
mimics the effect but must be done on both
sides of the flow switch electronics as your magnetic
pen or screwdriver may have +ve or -ve charge.