[rohrmann]

Also, cold water enters the water heater tank at the lower water connection, no check valve there, and the hot water exits at the upper water connection, and what appears to be a nipple will be the check valve. You should be able to purchase a new one at most good hardware stores and some big box stores, if replacement is needed. I would also caution, if replacement is needed, go with the brass valve instead of plastic. They can be a bear to remove, and when I installed a new water heater years ago, even with the water heater out of the trailer, it still took a 12" wrench to unscrew the valve, as it had hex flats that a wrench would work with.