Why my boiler not ingiting?

My boiler is Mynute 14se model.
Just before the start of winter, I have noticed that my boiler is not igniting. I switched it off and removed the cover. When the cover was removed, I switched it on, and there you go, it ignited. So I put back the cover, and it stop igniting again.Now, it won't ignite even if the cover is removed. What could be the problem?