rv2go wrote:
There is a check valve in the hot water line after it leaves the tank. It does go bad. Mine was located right at the tank. Yours may be there or a short distance away. Since I do not winterize, I just remove the small plastic plunger and replaced the case.
If you winterize, you will need to replace the check valve in order to keep from filling the tank.

Hot out on tank (top)........nipple that is screwed into tank is the check valve.
They are cheap junk..plastic plunger/spring/o-ring assembly. Clog up, jam, o-ring gets dislodged---no hot water can flow out.
You can gut them and just use the nipple
You can replace.........and probably have same issue again
You can gut them and install a shut-off valve on hot out (close when/if winterize) and not have issues anymore