If you only have one bypass valve, you'll have a check valve on the hot water output. It will look like a pipe nipple, but the insides is a one way. Those are notorious for sticking. I took the insides out of mine, making it a straight through, put it back on and added a Flair-It three way valve like the other one, so now I have an "old style" bypass system.
2013 F250 XLT
I now have a Keystone Outback, but I try to help when I can.
Bitter Gun Owner