I learnt about how photocopiers work in physics and i think laser printer work in the same way. It works because of static electricity. Negative charges are placed onto the paper in all the relevant places, so for example if you had a big X on your page it would but lots of positive electrons on the paper the paper would then go to the toner where it blasts black powder on to the sheet of paper, this powder is naturally negatively charged so it sticks to the paper in the correct places. The paper then goes to the heater where it gets heated to make sure the powder or ink is burnt on, this is why paper is warm when it comes out, this could be you problem. I think it could be that some powder has stuck on the heating element.
Hope this helps