Advice on a pool not fully priming..

[llcoolcal]

The facts- 20000 gal salt pool
brand new 2 hp pump which replaced the old broken one
brand new Hayward filter
not fully priming hence the pool vac (18 months old) hardly moving and not moving around sucking up the dirt on the bottom
the guy who replaced the pump said although rare the filter was faulty- so the store exchanged it
still its not fully priming and pool vac hardly moving-
when I remove the filter and turn the pool back on the outflow is strong and the pool vac working like it used to -its only when I put the filter back in it slows right down again

Thoughts? ideas? Miracles?

 

[mknauss]

Typically a symptom like that points to a dirty filter. That can be from algae in the pool that is quickly plugging it.

Another item can be the filter is plumbed backwards. Check that.