Ultimates do not Lock out, The fault is either, Fan not producing enough air pressure, Air Pressure Switch Faulty, No Ignition spark, faulty electrode or HT Lead, or Ign PCB, No Gas to pilot burner, blocke injector or pipe, or faulty Solenoid coil on Gas Valve
This is a Job for a Registered Gas Engineer
www.gassaferegister.co.uk
will assist you to find a RGI near you
www.elanar.co.uk, August 2009