One other potential cause...
I've been known to suffer from CRS before
If you winterized, did you turn the valve for the anti-freeze injector (the short hose and valve at the water pump inlet used for pumping anti-freeze in the system) to the "off" position? If you inadvertantly left in the "on" the position after using it to pump anti-freeze through the fresh water system, all your pump was doing is drawing air through the open hose as opposed to water from your tank. Just one more thing to check...been known to happen (don't ask me how I know