Problem solved DW is happy!!! Solution, the brass hot outlet on the tank contains a simple plastic one way valve (Check Valve as mentioned) above, to prevent return flow into the tank. The control spring is held on the valve stem by a pressed on plastic retainer. the retainer had popped off, the spring and retainer are somewhere in the hot water tank (forever). The valve itself had jammed and plugged the outlet. $25.00 at the RV parts counter fixed the problem. As usual you have to buy the whole fitting.
Thank you for your help!!