What can cause a pump not to pump water?
(1) A clogged impeller which does not allow for the flow of water or, most often, (2) it is caused by an air leak on the suction side of the pump. This could be the mechanical pump seal, o’rings or gaskets that are beginning to fail, or could be loose pipe fittings going in to or out of the pump. Valves before the pump could have bad o’rings or need new packing, depending on the type of valve. Underground plumbing leaks on the suction side or a bad skimmer are also possibilities, although fairly remote.