We recently replaced our "came with the house" sand filter after having that problem, as well as the multiport valve being stiff and the drain plug threads stripped...figured 3 strikes yer out. Well, the old laterals had no major damage, but the sand that came out was obviously finer than the sand that went in...so replacing sand would have helped a lot. We figured with the other 2 problems it was best to cut our losses and replace the whole beast for $250 + sand.