We could not keep water mixture in the heat exchanger on the 3MG30F Yanmar. After checking everything we thought about the hoses going from the engine to the water heater and upon pulling one out found that they were rotten and needed replaced. After doing this we are up and running. Anyone with a boat having 8 to 10 years of use might want check these hoses before you have a problem. Thanks for the reply of help. Nathan 'Brothers' Dream' 1986 Hunter 34