I find that the Nova center post sticks down slightly and when it is connected to the Twist it can be rocked back and forth, even though it works well. I think the center post keeps it from seating well on mine.
To clean the head; I unscrew it and rinse the wicks under warm running tap water. Then I put it in a glass and cover it with a couple inches of Distilled Water and put it in the microwave for 3 minutes to boil the wicks clean and let it soak for another 5 minutes or so. I pat the wicks dry with paper towel and then dry burn. Wash and dry the other parts and dry with paper towel. I`m sure that this is more than what is necessary, but it keeps me happy. You don`t have to do this if you are happy with just a rinse.
When I have problems with a wick or coil (I haven`t yet) I am going to re-wick with cotton. I won`t be able to dry burn then because of the cotton. I am also going to even out the center post "one of these days"! Lol
These are the best of anything I have tried so far. I love 'em!