Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
CH Demand
CH temperature control turned to MAX
Disconnect inline connector to flow switch
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the resistance across the pins of the inline connector which connects to the flow switch (see note)
Expected resistance continuity / zero resistance.
Note.
If there is no flow switch fitted on the appliance then select 'Resistance as expected'