Set Appliance State:
Set Multimeter to AC Voltage 
Isolate Mains Power to appliance as per TOPs P4
Boiler Operating Switch / Programmer set to HEATING and WATER
Gain access to PCB (use insulation mat as necessary)
Boiler Operating Switch / Programmer set to HEATING and WATER
Gain access to PCB (use insulation mat as necessary)
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure the voltage across connection 1 (Grey wire) on connector X10 and the Neutral (Blue wire, connection 2 marked N) on connector X7 on the main PCB..
Repeat the measurement using connection 2 (White wire) on connector X10 and the Neutral (Blue wire, connection 2 marked N) on connector X7 on the main PCB.
Repeat the measurement using connection 2 (White wire) on connector X10 and the Neutral (Blue wire, connection 2 marked N) on connector X7 on the main PCB.
Isolate as per TOPs P4
and refit as necessary