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....
You need to post Brand and MODEL of water heater. If you have the Atwood EXT model, your mixing valve is clogged. Also, check your whole house water filter if your model came with one. The whole house should affect both HOT and COLD, but I have had some that affected the HOT worse than the cold. Doug