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Hi my name is Robert...
Normally you would have a hot, cold and bypass. The hot and cold should be open or valve handle running with the pipe and the bypass closed or valve handle against the pipe. IF the water in the tank is HOT but the line coming out of the tank is not then you might have a failed check valve on the tank. The check valve would be about 3" and be plastic or brass, it screws into the hot or cold port and then the lines from the RV hook up to them. What can happen is the spring and disc can fall out and block the flow of hot water, below is an example of where it would be located. If you see that I would drain the tank, shut the water heater off and remove, you should only be able to blow air in one direction through the valve. Beyond that if you have an outdoor sprayer make sure the valves are OFF have seen some issues when they are left open. IF you still need help please get me the make and model of the water heater... Hope this helps.... Robert