I have a 2004 winnebago Journey 36G. I have replaced the check valve behind the water hearer a couple of time. Today while unwinterizing all was going well after flushing the water heater and lines....
There is another check valve. At least there is on my Journey. Check the pluming diagram from Winnebago. I had to remove the metal panel that held the city water inlet and other valves. It was a long reach to get to it. I first called Winnebago service. They were most helpful.