Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn DHW isolation valve to "OFF" position underneath the boiler
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the boiler still attempt to fire after self-check & purge cycle has completed?
Cancel the purge cycle if required, click HERE for instructions.