Set Appliance State:

Turn Hot Water Tap On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset the appliance.
Allow the boiler to complete its self check and begin the ignition sequence. Does the fault reappear or does the boiler ignite?
Boiler resets and ignites - retest appliance
Boiler will not reset or resets but returns to fault code