Set Appliance State:
Set Multimeter to AC Volts 
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Gain access to PCB (use insulation mat as necessary)
Boiler Operating Switch / Programmer set to WATER only
Gain access to PCB (use insulation mat as necessary)
Boiler Operating Switch / Programmer set to WATER only
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure the voltage across connection 3 (Grey wire) on connector X3 and the Neutral connection 2 (Blue wire) on connector X7 on the main PCB.
Isolate as per TOPs P4
and refit as necessary