WhisperFlo 1 1/2 hp pump won't prime on its own anymore!! It was intermittent at first, but over the past few months it has gotten to the point where it will not prime without filling it with water ( sometimes 3 or more , that is shutting everything down, filling the pump and turning it back on, before we can get water flow). The skimmer basket is clean, the cartridges in the Pentair Clean & Clear plus 420 are clean and the manifold is seated firmly, I just replaced the gasket on the filter housing & the pump lid gasket (pool lube included) after installing gaskets and refilling pump, it primed fairly fast, however after shutting down for the night, it wouldn't prime....again!