Set Appliance State:

DHW Demand
DHW Selector in Maximum (+) position
CH Selector in Minimum (-) position
ON/OFF Switch in ON position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the boiler get to the sparking stage of the
ignition sequence or does the fault code reoccur?
Fault code reoccurs - Continue fault code diagnosis.
Sparking present, fault code does not reoccur - Continue testing appliance through full model.