chaffoteaux calydra 80 keeps locking out?

hi.......i have a chaff boiler that keeps locking out on no flame detection,the boiler starts the ignition sequence,the burner assembly lights but only on the right hand third of the burner (where the igniter is) the flame does not always track across the burner (where the ionization electrode is located) thus locking out on no flame detection,from what i can see its when it is runninig in 1/3 low flame,i've removed and cleaned burner assembly,injectors,heat exchanger & fan,checked flue is clear in & out,all ok,checked burner pressures,they are ok according to chaff tech help who didnt have a clue,removed and cleaned gas valve/solenoids even though they was clean anyway,it does this evey day wether on heating only,water only,or both,any help would be greatly appreciated,i'm ready for ragging it off the wall and throwing it out of the window!