Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
Gain access to flow switch inline connector
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
With no hot water demand measure the voltage between the green and black wires on the inline connector.
Voltage should be either 0V or 5V DC.
Voltage should be either 0V or 5V DC.
Isolate as per TOPs P4
and refit as necessary