I had the same problem with the locking out and failing to light my problem was caused by the ignition plug (like a spark plug) this had been incorrectly fitted from new. I had to get a Baxi engineer out but was under warranty then.This will not be your last problem i am afraid, you will have...
I have a powermax 155x boiler that whistles every morning i have had the fan changed about 3 months agoad it went away,but it has just started again the noise happens when the boiler is cold the whistling goes off after a while i have seen somone mention a gas valve as the noise can be heard...