Something is blocked. It could be your lines, your pump, your filter, or your multivalve. Does the pump work when you set the multivalve to WASTE? If yes, the problem isn't in your pump or the lines to your pump, but in the filter or multivalve.

If you disconnect the pump from the filter does it pump? If no, then your problem is in the pump or the lines to it. Plug your drains then disconnect the return line from the pump. Slowly open one of the plugs in the drain. If the water flows freely, you've now isolated the problem to your pump.

Diagnose by eliminating where the problem cannot be. Whatever is left is the source of the problem.