Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Gain access to PCB (use Insulation Mat as required)
Main On/Off Control in the On position
Heating Control to Heating & Hot Water
CH Temperature Control to Maximum
Remove plug X25 from Relay Board
Remove Yellow plug X12 from Motherboard and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

If a fault is displayed press boiler 'Reset' button.
Measure Mains Voltage across X25 on Relay Board.