I recently moved into an old home (circa 1920), and the shower would get cold after about 10 minutes of use. We would constantly have to lower the cold water during that time until it was completely shutoff, and then the hot water would run out completely.
We had a plumber in and they thought it was likely a broken dip tube, so we went ahead and had the ~7 year old hot water heater replaced with a new 40 gallon / 40000 btu tank.
The hot water still ran out after about 10 minutes of use. I turned up the temperature on the hot water heater, which made the initial hot water hotter, but the water still ran out in 10 minutes.
I've done research and have read that it is possible that a hot water pipe might be connected to a cold water pipe. I think this might be a possibility, but how would I go about determining if it is?
Any other thoughts on this would be great as well.