It's easy to cross-thread / misthead the Novas, I do it to my top probably 40% of the time unless I follow the below procedure.. try this once it's empty, or next time you'r ready to clean it
Unscrew the bottom, and then before screwing it back on.. turn in the counterclockwise position a turn or 2 to ensure that the threads will seat correctly, then tighten.
this may solve your issue.. it may not