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Join Date: Apr 2006
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Easy, bad float switch. ALL float switches go bad. The electronic ones get a coating of crud and fail to trip, the mechanical ones jam. So far the only really 100% reliable way to rig a float switch, is to have a crew stationed in the bilge with his crotch just above the waterline. When the cold water rises, he'll let you know to turn on the pump. (Works best in icy water.)
Yeah, well...seriousaly, the best you can do is to have TWO float switches so that one failure won't stop the pump, and at that point with pumps being so reliable, might as well have two whole pumps in there.