Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to AC Volts 
CH Demand
Gain access to PCB (use Insulation Mat as required)
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Boiler ON/OFF switch ON.
Measure the voltage across terminal marked Lr (Return) on terminal strip marked ST8 and terminal marked N (Neutral) on main terminal strip marked ST12 on PCB.
Measure the voltage across terminal marked Lr (Return) on terminal strip marked ST8 and terminal marked N (Neutral) on main terminal strip marked ST12 on PCB.
Isolate as per TOPs P4
and refit as necessary