Lindsay:
The two water hoses that run from the engine to the water heater are lines filled with engine antifreeze/coolant. This coolant will be at 180 degrees F when the thermostat opens on the top front of the engine. This usually happens after 10 minutes or as soon as the engine block is hot. This coolant loop then runs into the water heater, through a heat exchanger loop in the water heater and then back to the engine. This is a fully closed loop and the coolant is being pumped by the engine. if your water heater is not getting hot or warm after 20-30 minutes, then this coolant line is blocked or it could be pinched in the sail locker where it makes a hard 90 degree turn around the stern to get to the water heater. If your engine temp is not over heating, then your thermostat is most likely working and opening. If it did not open, then coolant would not flow to heat the water heater. I would look for a pinched line by following the entire run and checking the hose. Also, when the engine is running, and hot, check the hose temp in the sail locker or right at the water heater. These are the black rubber coolant hoses, not the water hoses. If these are not hot then you have no flow back to the water heater.
If all else fails, you can use this reason to drain the coolant and flush it all out and add new coolant.
Can you tell us if there is heat at the coolant hose as it enters the water heater?
Hayden
