I have an expansion tank installed in the cold water feed of my water heater. I suspect that some of the warm water in the expansion tank is being drawn into the domestic cold water of my faucets which doesn't allow this cold water to be as cold as it should be. Is this possible and would a check valve on the cold water side of the expansion tank help. I have a checkvalve in the pipe that goes to the mixer valve.

Hey Art,
Yes, a check valve installed upstream from the expansion tank will prevent any of the hot water from expanding into the cold water main. Regards, tom