Quote Originally Posted by 686 Shooter View Post
On my Mega S the bowden tube was not tight against the nozzle. This will contribute to your problem. Also the tube itself is not of great quality, I replaced mine with some Capricorn tubing.

To ensure your bowden tube is tightly sealed against the nozzle heat the hot end to 200 degrees, loosen the tube fitting on the top of the hot end by 3/4 to 1 turn. Push the tube in until you are sure the tube is touching the nozzle then tighten the fitting. This will give you a nice compressed seal and avoid any leaks. This solved the problem for me.

I also found that it helped to push the filament into the hot end until you get some coming out then quickly pull the filament back.
I hope you mean that your bowden tube was not against the heat break, rather than the nozzle. If it's against the nozzle, it's going too far into the assembly. It should stop well clear of the heater block and only part way into the heat break.