Set Appliance State:
Set Multimeter to AC Voltage 
Isolate Mains Power to appliance as per TOPs P4
CH/HW switch in HW position
Ensure that the boiler is cold and ready for Pre-heating
Gain access to PCB (use insulation mat as required)
CH/HW switch in HW position
Ensure that the boiler is cold and ready for Pre-heating
Gain access to PCB (use insulation mat as required)
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure mains voltage across the blue and brown wires marked N and L at the terminal block to the rear of PCB 26.
Isolate as per TOPs P4
and refit as necessary