Well we got the water heater installed last week-end and had problems, I installed the new heater connecting the hot, cold, 120 Vac then hooked the "in and out" for the heat ex-changer, checked and added anti freeze and went for a ride, engine overheat light and horn came on, we shut down the engine and raised sail and headed back to the marina, a mechanic friend came to our aid, check the water level in the engine, found none, the short story, I cut a couple of inches off each of the heat ex-changer lines added water and bravo we're off.