I have a 40 gal natural gas hot water heater this is almost 10 years old, and have had no problems with it since I purchased the home 4 years ago. Just recently, my fiance has been complaining because there is no hot water for her shower, while my shower, usually taken 1/2 hour earlier on workdays, is fine. I've turned up the water temp (which was set to medium)to almost high, which results in a much hotter shower for me, but still little to no hot water 1/2 hour later, and the duration of the first shower doesn't seem to matter (2 min or 15 min, the result is the same). I've tried flushing the heater several times. Is there anything I'm missing?