Hi ATV;

If a pump spins, but doesn't pump, you can test it by filling the strainer basket FULL, and turning the pump on -- briefly -- with the lid still off. If the pump / impeller / diffuser are all correct, the water will more or less instantly be pumped out. If it is not, there are two possible problems. ONE, you could have a valve closed or a total obstruction in the piping close to the pump. Or TWO, the impeller / diffuser were not installed correctly.

If the pump DOES pump the water out of the basket OK, you may have a priming problem. This can be caused by a long pipe between the pool and the pump that has filled with air. Some pumps -- like the Hayward Super Pump --are very good about 'priming' -- pump the air out and 'picking up' the water. Others, like the PacFab / Pentair Challenger Hi-head models are very bad at it. But, you can run the pump a long time to see if it will pick up so long as
=> there is still at least a little water in the pot, and
=> the water / strainer chamber / volute (where the impeller is) are not getting hot.

If you do not 'pick up' prime after 30 minutes or so, you may have a suction leak around the strainer pot lid, or the piping connection, or the suction piping somewhere.

Ben