Possibe air in the line to a seldom-used faucet...
Wallace-If a tank went dry recently, you may have a large air bubble in the line to an seldom used lav faucet (i.e., swim-platform shower). Unlike water, air compresses and the pump may not shut off. Bleed each h/c faucet throughout your boat. Do this cheep check before you consider a pump repair.Enie April