Set Appliance State:

Mains Power Off
Ensure there is no demand for either CH or DHW
Selector switch in ON position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

When power is switched on the boiler will run a self-check which should follow the sequence in the image above, with the exact values changing dependant on boiler type and output, if the display does not progress from the initial self-check CLICK HERE.
At the same time the pump and fan will start to run and then the display will show 00 indicating the boiler has completed its self-check and entered stand-by, awaiting a request for heat.
Note:
Fan and pump will continue to run after self-check is complete (up to 4 minutes).