Set Appliance State:
Gas Off
Set Multimeter to AC Voltage 
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Boiler Operating Switch in HW position
Gain access to terminal strip (use insulation mat as necessary)
Boiler Operating Switch in HW position
Gain access to terminal strip (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 (White wire) and Neutral connection (Blue wire, marked N) on the L/H connector block.
Isolate as per TOPs P4
and refit as necessary