Lose sea water flow in my M25
Something has happen twice this year that has never happen before (I've had the boat for 6 years). I go out sailing, the engine runs fine. After I sail and start the engine, I get no water flow. I check everything and find nothing wrong (no weeds or blockage). I disconnect inlet to the water pump and I suck the water to the pump, reconnect it and the engine runs fine. It's like I am loosing prime to the pump when I'm sailing. I have a heat exchanger system. Any thoughts?? Thanks in advance for any help.