Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to AC Volts 
Locate the Grey wires in the wiring centre
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure the voltage to earth on the Grey wire.
This wire supplies a permanent mains voltage to the micro switch in each Zone Valve.
Is mains voltage measured on the grey wire?
Note: The colour and position of the wires will vary between systems and components.
This wire supplies a permanent mains voltage to the micro switch in each Zone Valve.
Is mains voltage measured on the grey wire?
Note: The colour and position of the wires will vary between systems and components.
Isolate as per TOPs P4
and refit as necessary