Air in system

I seem to be getting air in the system.  Upon start up a lot of bubbles are forcefully expelled from the inlets.  I replaced the filter fins last year (and checked that they were fine and tightened them).  I replaced the spider gasket as well.  The only other change from last year was a new heater was installed.  Any suggestions?

Hi TMajic,

I would watch our following 2 Videos as they should help

And here’s one more =)