... worse. I replaced the water heater and that did nothing. I replaced all the cartages in the (single handle) valves for sinks and showers and that did nothing. My house does not have a hot water recirculation system. So I turned off the cold water input line going into the water heater completely and then turned on the hot water tap in a sink (dual knob one). Cold water rushed out of the hot water tap! The only other place inside my little house where the hot and cold could mix is inside your washing machine. But it's got a dryer on top and it's inside a tight closet and cannot be pulled out to simply turn off the water lines going in, without coming up from under the house just behind it. So I asked the Sears online chat help if it is possible that the washer is allowing the hot and cold water lines to mix, even when the machine is turned off? And the answer they gave was that it is impossible. So how is the cold water getting into the hot water line?