I have no suction to vacuum -- what’s wrong?

First, ensure that the pump is properly primed (minimal to no air in the basket area). Second, confirm that the filter pressure is operating at normal levels. If it's low, you should check and clean skimmer and pump baskets, check and clear suction lines of any possible debris or blockages, and possible check and clear any pump impeller obstructions or debris. If the pressure appears high, clean or backwash the filter according to manufacturer recommendations and then confirm that the pressure has resumed to normal operational levels.