Set Appliance State:
Mains Power Off
Set Multimeter to AC Voltage 
CH Demand
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure the Voltage across the Room Thermostat /
External Controls terminal marked ON and the neutral (N)
(Blue wire on the main connector block).
Note:
If a Room Thermostat\External Controls are not fitted there will be a Link Wire connected between the connections marked ON and HW.
External Controls terminal marked ON and the neutral (N)
(Blue wire on the main connector block).
Note:
If a Room Thermostat\External Controls are not fitted there will be a Link Wire connected between the connections marked ON and HW.
Isolate as per TOPs P4
and refit as necessary