[JRTJH]

The bypass valve is located on the back of the water heater (the inside, center part of the heater) and is attached to the cold water inlet port. That is the lower inlet to the water heater. You'll probably have issues locating it as it's often a 1/4 turn valve handle positioned on the inside of the fitting, so you've got to be "standing on your head, left foot forward, tongue in right cheek and pretending to be cross-eyed to see it".... Here's a picture of a couple of water heaters so you can get an idea of what you're looking for. In the second photo the valve is located at the lower fitting on the end of the blue PEX tubing. Well hidden unless you know what you're looking for......