Have you checked the pressure to the nozzle, is it set as in the operating manual? Have a look in the manual and see what nozzle is recommended. If you are using a hollow pattern nozzle, try a solid one and vv.
When you now refer to "tripping out" do you mean this or that the flame becomes unstable and blows out.
Have you tried a new nozzle? Is the correct size nozzle fitted ie one which matches the boiler. Check the manual and see if the burner has been replaced with one which is too big for the boiler. Have you checked the relationship between the nozzle and the air spinner plate does this match the spec in the manual?
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!