You have a spring loaded valve inside the water manifold. Open the manifold and make sure that that valve is closing. Then or first make sure if you have a by-pass valve be sure that is almost closed.these will make sure that the water is going through the heater. Also remember you shouldn't be able to feel any hot water at the returns. That is part of what these valves do. They help keep anyone from getting scolded by too hot water. The water at the return should be no more than 7 to 10 degrees hotter than when it goes into the heater.