I need advice. I have a three- story townhouse (four-story of you count the finished basement) that is just three years old. When I run the third floor master bath shower, I usually run it for about two minutes so that the hot water can come up from the water heater in the basement. For about the past month, the water for this particular shower does not get hot regularly. I can get hot water everywhere else in the house - even in the third floor sink (I tried running the sink at the same time I run the shower, and hot water comes out of the sink but not the shower). Is this a major plumbing issue, or something simple I am overlooking?