Atwood water heater problem

My flame is not perfectly blue either. My problems with Atwood water heater not getting hot water is the mixing valve on the back of the water tank. It mixes the cold water with the real hot water coming from the heater. The valve is suppose to give you extra capacity a 10 gallon equals 16 gallons. Because of the mixing. What happens is hard water will form calcium flakes at the mixing valve this blocks the hot water side of the mixing valve off--so all you get is warm or cold water. The fix is to remove the valve and clean the opening out. The easy part is cleaning the valve the hard part can be getting to the valve. Google Atwood mixing valve also check to make sure your model water heater has the mixing. Good luck.