camray 5 stand alone combi?

Hi
i recently had trouble with my camray combi oil heater. It was working a few days ago but it took some time to fire up from the boiler. Once it started it worked ok for around an hour, but then started tripping out once restarted after 2 -3 minutes. I then left it for a few days and when i tried again it would not fire up. the extraction fan is working fine, the water pump ok, motorised head ok, oil ok.
For some reason it just wont fire up, how can i check if the ignitor is faulty, i believe it may be the injector nozzle but i cant find anywhere that shows me how to remove it, And yesterday the lockout light has just come on, i tried resetting but it is still on, please help.