Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Remove connector on pump flow switch (red wires)
Remove connector on pump flow switch (red wires)
Measurement:
Measure resistance across pump flow switch
Resistance should be open circuit.
Mains Power On
Selector switch to DHW position and turn on hot water tap.
With pump running resistance should now be short circuit.
Resistance should be open circuit.
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Selector switch to DHW position and turn on hot water tap.
With pump running resistance should now be short circuit.
Isolate as per TOPs P4
and refit as necessary