Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to AC Volts 
CH Demand
CH temperature control to max
Gain access to PCB (use insulation mat as necessary)
Ensure external controls are calling
Gain access to PCB (use insulation mat as necessary)
Ensure external controls are calling
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure voltage across terminal marked 3 and the terminal marked N on the controls installer interface.
If no external controls are fitted then a link should be present between terminals marked 3 and 4 on the installer interface.
If no external controls are fitted then a link should be present between terminals marked 3 and 4 on the installer interface.
Isolate as per TOPs P4
and refit as necessary