Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Gain access to PCB (use Insulation Mat as required)
Main On/Off Control in the On position
CH Temperature Control to Maximum
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

Observation:

If a fault code is displayed press boiler 'Reset' button.
Remove Pump inspection cover. Is Pump running?