determining the cause of hot water issue

evolve · Jan 3, 2014

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.

Thanks

thedrainguy · Jan 3, 2014

Just trying to eliminate a couple things.

Is it just the shower where you lose the hot water quickly or does it happen in the kitchen and bath sink as well.
Matt

Mr_David · Jan 3, 2014

Going to presume you have a 2 handle shower fixture and not a single handle unit.
Try shutting cold water supply to the Water heater. then turn on the hot shower valve and see if any water comes out.

Maybe the cold supply going into WH is backwards. Connected to the hot side.
this can easily be checked by running hot water and the left supply on heater should be getting hot , not the right one ,of which should be the cold supply with a valve.

evolve · Jan 3, 2014

@thedrainguy I just ran the kitchen sink for 35 minutes and the hot water ran out.

@Mr_David: I do have a 2 handle shower fixture.

The left supply is hot to the touch when I have hot water.

I'm fairly sure that the supplies are hooked up correct, the right supply is coming directly from the water supply pipe coming into the house (non-finished ceiling so I can see all the pipes).

I'm wondering if I should just try a new shower head, I'm not sure how many gallons per minute this one is...

havasu · Jan 3, 2014

Not saying that this is your problem, but a member here recently reported that their brand new water heater was found to be defective, and your symptoms are exactly what he described. You should not run out of hot water in 35 minutes, and a shower head will not solve your problem. .