Originally Posted by crisen
To the OP original question, if you have any hot water at all, like the one cup you say you get it shouldn't be a by pass valve problem at all. If so how did that cupful get hot?
The valve is between the the inlet and outlet of the HW heater. With all 3 open the water just above the heater gets warm but when the water is turned on it travels across the bypass instead of going all to the water heater. Closing the bypass forces cold water into the heater and the hot water out of the heater.
Until it happened to us, my thinking was the same as yours. It happened on our first trip and I knew exactly where to go to resolve the problem.
Thanks to the forum for helping me, glad I could pass it along.