Are you saying that there's enough water in the bilge to completely submerge the pump, but when you turn it on none comes out the discharge hose?
Been like that since you got it, or new development?
Before spending any money I'd rule out a wiring problem by connecting the pump directly to the battery, see if does better.
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"The metric system never really caught on in the states. Unless you count the increasing popularity of the nine millimeter bullet." -- d. barry