leveled wrote:
So how should I manage these ? make sure they are all loose (the plastic
screw) ??

When you're in the vicinity, loosen the cap. If they're working
properly AND there's air in the system, there'll be a
"hisssssssssssssssssssss, thump" as air leaks out and the valve closes.
Probably best to turn the pump off before doing this.

Leave the caps screwed down normally 'cos they're not 100% reliable &
are probe to leak water all over. A good system shouldn't collect any
air in normal operation, so the ususal practice is to leave the cap
open for a week (after refilling) or so until all air is removed, and
then close them. If they're in the loft, ensure they're insulated over
to avoid freezing & splitting them (and everything else besides).