You should be able to press the button with the cap off and a loaded herc, and if you just watched it instead of hit it, it should produce visible vapor. If that's not happening with fully charged batteries, a coil that is seated firmly in the bottom of the chamber, then there has to be a fault or poor connection somewhere. You squished your coil so it doesn't slide up while you draw, right? If you don't have any wear on the contact points of the ceramic rod, and it's in the correct place, and producing heat, I don't think that is your culprit. You only have a 3.7V rod? You'll need to hold the button for quite some time before the 3.7 rod heats up and produces vapor. Make sure the button is staying lit the whole time you're preheating; you may need to let off for a quarter second and re-press to keep power to the Herc while warming up. The 3.7V rod will not put out as thick of vapor as the 7.4 rod in my experience.