Set Appliance State:
On/Off Switch OFF
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Disconnect the flow switch at the inline connector
Test to be carried on the connector leads that run to the flow switch
Disconnect the flow switch at the inline connector
Test to be carried on the connector leads that run to the flow switch
Measurement:
Test 1.
Measure the resistance of the flow switch at the inline connector. Resistance should be open circuit.
Mains Power On.
CH demand.
Test 2.
Repeat test. Resistance should be closed circuit.
Measure the resistance of the flow switch at the inline connector. Resistance should be open circuit.
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
CH demand.
Test 2.
Repeat test. Resistance should be closed circuit.
Isolate as per TOPs P4
and refit as necessary