Just guessing that maybe your bypass valves are not in the proper position. Don't know what the 4th valve is for, but the valves to the
water inlet and outlet need to be open and the bypass valve needs to be shut. Imagine the capital letter "H" the valves on each side (the vertical sides)need to be open and the line joining the 2 sides(the bypass valve) needs to be shut. Just the opposite for winterizing. Happened to me a couple times with the exact symptoms you described, when valves were in the proper position-problem solved. Gary
2018 coachmen leprechaun class c 2008 KZ spree 260FL