Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
Gain access to PCB (use Insulation Mat as required)
Boiler Switch in ON position
Central Heating switch in OFF (central) position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Is there mains voltage present across connector PL3 connection 3 (red wire) and connector PL1 connection 8 (blue wire)?
Note:
Boiler may go to lockout.
Switch OFF power and press reset button to cancel lockout.