1. Remove input hose from pump to insure water is getting to it. If not...clean out hose and through hull.
2. Remove hose from pump to heat exchanger...turn engine on briefly to unsure pump is pumping water. If not ...replace pump gasket and replace impeller while you are at it. Try again.
3. If you now have good flow out of the pump but not out the back of the boat...the you have a blockage in the heat exchanger or mixing elbow, which should be removed and cleaned.
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