Ok, I have one other thought for what might be wrong but am only going on my experience with the 901 so I hope it holds true for your model. I was having trouble with a super easy,non-resistive draw with little vapor produced one day and finally figured out that the mouthpiece wasn't pushed all the way onto the atomizer. It felt like I was just sucking air. That particular mouthpiece was just really tight and did not want to seat correctly. Looking at it I could tell there was a little more room it could move down and it took a real hard push to get it there even though I previously thought that I had it down as far as it would go. In other words, make sure your mouthpiece is seated down onto the atomzier as far as it is supposed to go.