Set Appliance State:

Mains Power Off
Run hot water tap until water cool then turn tap OFF
DHW temperature selector to MAX
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to carry out ignition sequence and burner to ignite.
(if boiler returns to lockout before ignition select that option below)
While observing the burner through the sight glass turn the DHW temperature control to MINIMUM to disable preheat.
Does the burner extinguish immediately or does the burner stay alight after demand. Does the fault code reoccur?