Hi I am new in the rv world, got ours end of last season. I just tried the hot water heater last week and allowed it to try and heat for about 45 min before I tested it. When I turned on the kitchen sink it was super hot, then it would go cold and then warm hot and cold and back and forth. Turns out there is valve under the kitchen sink that goes to the water heater and mine needed turned so it would not mix hot and cold water together and keep the two separate instead of blended. I turned one knob and all was perfect! I think it is there for winterizing purposes and that's why it was turned to how it was. Just my guess. You might take a look and see if you have the same thing happening.
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