It sounds like it is "primed"
You dont really "prime" a HOT filter. You can pour some water on the intake tube, and that sometimes helps, but generally, the filter draws up all the air from the tube all by itself. (as long as there is water in the filter)
...I wish I knew what was wrong with my filter too.

At least I have another filter constantly on the tank, but it doesnt get the water nearly as clean with just the 1.
Cap-hits, not Cafits.