Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
Boiler ON/OFF switch ON
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure the voltage across terminals marked 1 and 4 on the terminal strip marked ST13 on the PCB.
Isolate as per TOPs P4
and refit as necessary