Set Appliance State:
Set Multimeter to AC Volts 
Isolate Mains Power to appliance as per TOPs P4
CH/HW switch in CH position
Gain access to PCB (use insulation mat as required)
CH/HW switch in CH position
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 neutral (blue) wire on the mains supply connector block, and one of the spaded white wire connections on the HW/CH switch.
Repeat using the other white wire spade connection to the switch.
Repeat using the other white wire spade connection to the switch.
Isolate as per TOPs P4
and refit as necessary