Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect 1x electrical connector to the DHW flow switch
Isolate the incoming DHW supply to the boiler by closing the valve on the furthest right
Isolate the incoming DHW supply to the boiler by closing the valve on the furthest right
Measurement:
Measure the resistance across flow switch terminals.
Expect open circuit.
Is the resistance measured as expected?
Expect open circuit.
Is the resistance measured as expected?
Isolate as per TOPs P4
and refit as necessary