1.5hp pump with 1.5'' pipe?

[mas985]

The pump was sucking water, but it wouldn't fill up the basket to the lid

What is the filter PSI?

If it is low, then there is probably a blockage in the suction line somewhere.

If it is high, then the return side might be blocked somewhere and could be the filter.

Either situation can lower flow rates such that the pump cannot expel the air in the pump basket. However, a suction side blockage will also tend to draw in air from the pump basket lid and other places.

[joenj]

Does the filter have a recirculate position? Bypass the filter to see if the pump primes.