Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
CH Demand
Gain access to PCB (use Insulation Mat as required)
Ensure all external controls are calling
Ensure all external controls are calling
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure the DC voltage between the right hand terminal of the 24v external controls connection and a suitable earth.
Expect 24 Vdc.
Expect 24 Vdc.
 pcb in situ.gif)
 connector x100.gif)
Isolate as per TOPs P4
and refit as necessary