Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
DHW Demand
Disconnect the white lead from the orange lead at
the inline connector and make the Orange lead safe
Disconnect the white lead from the connection
marked NO on the air pressure switch.
Attach -ve probe via croc clip to spade connection on white lead.
Attach +ve probe to the other disconnected white lead.
Boiler thermostat to OFF
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Multi-meter should be showing open circuit
Turn boiler stat to max, after approximately 4 seconds multi-meter should show closed circuit as pump runs and operates flow switch.