We had a new hot water heater put in about eight months ago. Initially, hot water from the new water heater was almost immediate, even in our most distant shower and stayed hot. However, after a couple of weeks, we started to notice that the water would quickly turn to luke warm or warm after initially being hot. Water from all of our faucets that have a hot and cold valve runs hot. However, water from any faucet that has a single mixing valve behaves as described. Moreover, if you are taking a shower and run hot water from any other faucet in the house, the shower goes from the luke warm or warm state to ice cold and stays that way for a long time, as though the hot water line has filled with cold water. Checked the pipes coming from the water heater and their temp does not fluctuate -- feels hot the whole time. Does anyone have any bright ideas?