I am at my wits end on this one so would VERY appreciative if someone can figure this one out.

We have a two story house with basement with one shower and 40 gallon gas hot water heater (domestic) that has given us problems from day one in the 14 years we've lived here. The problem has been that first thing in the morning we get luke warm showers and have never been able to take two consecutive hot showers. The latest problem is that we have intermittent water pressures along with the normal hot water issue. This is the third (maybe fourth) water in the 14 years and currently have a GE 12 year heater. I have had every component of this checked out (t-stat, burner controls, flue, etc.) all check out. So please don't say check these, not being unappreciative but I know not the problem.

I recently replaced the mixing valve in the shower and now we have a new issue on top of the other, some mornings the water pressure is ridiculous low with next to no hot water.

My heater is located in the basement if I can figure out how to post a pic of lines I will but the hot water comes off htr to the house then there's a 90 off it that feeds our washine machine in basement (closest fixture to htr), dishwaser and sink both on first floor. The line continues after the 90 to feed the bathroom on second floor, sink is first with shower being furthest from htr.

My wife recently found that if we have the pressure hot water issue if she runs washing machine problem immediately goes away.

Anyone have any ideas????

thanks in advance