faulty pump?

Salinity is 1.026 and sitting in 7.5 inches of water. The tank is 4 months old with a large bioload. With the pump all the way up and the output valve all the way closed, it's still unable to push water more than 2 inches above sump water line. Pump is clean and free of debris or obstruction. I'm thinking the pump itself is faulty. The skimmer is only a few weeks old.