Rapidly Running out of hot water

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  • Rapidly Running out of hot water

    I recently moved into a new home that has a fairly new (May 2016) 50 gallon water heater plus a hot water recirculator pump ( Grundfos UP 15-42F and a Honeywell aqua stat L6006C set for 130, 5 degree differential.

    My problem is the hot water runs out way too early; about 10 minutes or less into a shower. The temp on the water heater for both the upper and lower are set to ~140 but the temp coming out of the nearest faucet starts at about 127 and rapidly goes down to ~99 in less than 7 minutes.

    This is what I've tried:

    Thinking there might be a crossover issue, I turned off the cold water supply to the water heater and turned on the hot water outlets in the rooms that had single levers. The master shower runs when I turn on the hot water. Not a lot, just enough to think you left the water on. I can push in on the stem and the water almost stops. Is this the cause of my running out of hot water?
    Thanks for your help.

  • #2
    To test for crossover or bad element, run the water till it gets cool at the faucet, leave it running and see if the outlet pipe on the water heater is hot, if it is you have a crossover problem, if it is also cool, you have a bad lower element or a problem with the water heater thermostats.
    I answer all plumbing and heating questions, all day long.

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    • #3
      Originally posted by Webmaster View Post
      To test for crossover or bad element, run the water till it gets cool at the faucet, leave it running and see if the outlet pipe on the water heater is hot, if it is you have a crossover problem, if it is also cool, you have a bad lower element or a problem with the water heater thermostats.
      At that same shower, I ran the water on cold and checked the pipe is hot. I am assuming the issue is at this shower? Would it also cause running out of hot water at the other shower and in the kitchen?

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      • #4
        You need to run the hot water until the hot water cools, then test the hot water pipe to see if it is hot.
        I answer all plumbing and heating questions, all day long.

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        • #5
          Ahhh... got it! Ok, the water in the other shower turned cool within 5 minutes but the pipe on the outlet of the water heater was cool.

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          • #6
            Okay that indicates, the problem is with the water heater, and not a crossover problem.
            It may be a bad lower element, or either of the thermostats upper and lower, or a bad dip tube.
            I answer all plumbing and heating questions, all day long.

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            • #7
              Earlier in the day, I checked the elements, 13 ohms each and not shorted to the case. With power off, tested each thermostat for continuity when adjusting the temp and each showed connect/disconnect on the meter.

              I have not checked the dip tube. It is a Rheem heater and the dip tube is supposed to be PEX. Just curious as to what can go wrong with a PEX tube.
              Thank you.

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              • #8
                I don;t know if it is the dip tube or not, dip tubes usually out last the water heater, maybe it would be best to let the water heater recharge and then do the test again, just to be sure the hot water was not used up before you started the test.
                Then once you have a cool outlet pipe, check to see how hot the water at the bottom of the tank is, by draining a little out from the bottom.
                I answer all plumbing and heating questions, all day long.

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                • #9
                  I tried this again today. The hot water pipe is lukewarm at best. I then took the temp of the water at the drain valve. It was about 85 degrees.

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                  • #10
                    Well it is not the dip tube, I still think it may be the lower element or one of the thermostats, you may have another problem. turn the water going into the water heater off, wait an hour and do the test again, this will eleminate leaking toilets and broken pipe under a slab.
                    Also can you see the discharge pipe from the relief valve?
                    I answer all plumbing and heating questions, all day long.

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                    • #11
                      If you can see the relief valve discharge pipe, is it leaking?
                      I answer all plumbing and heating questions, all day long.

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                      • #12
                        The relief valve pipe is not leaking. I do want to add something. I had two plumbers tell me it would be ok to turn off the power to the heater on the right to save electricity since I don't need 100 gallons. That water heater is on its last leg and I will be replacing it permanently or take it out of the equation all together once I get this issue resolved.

                        My question: Is leaving this in as a dead-head causing this problem?

                        I will redo the test tomorrow. Click image for larger version

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                        • #13
                          From what I can see. no but I do not see the recir, pump piping
                          I answer all plumbing and heating questions, all day long.

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                          • #14
                            Recirculating pump pic attached. Click image for larger version

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                            • #15
                              I repeated the test; no difference. I did notice that every time I ran hot water it was hot until the recir. pump kicked on. I unplugged it and the water turned hot again. Tried this four times just to be sure.

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                              • #16
                                Is the re circulation line tied to a hot water line? It should be, if it is tied to a cold water line, that is bad.
                                I answer all plumbing and heating questions, all day long.

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                                • #17
                                  As you can see from the pics, the line comes out of the WH and goes up the wall into the ceiling. What I don't know is where the other end goes to. I would assume the kitchen but there isn't anything there. I've checked the other sinks as well. The ceiling is finished and I would have to start cutting, which is a last resort.

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                                  • #18
                                    Try leaving the pump off for a while, it may be hooked up wrong. and it looks like it may be the wromg type of pump for a water system, it looks like a heating system pump.
                                    I answer all plumbing and heating questions, all day long.

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                                    • #19
                                      I have turned it off before and the kitchen and bedroom on the opposite of the water heater take 5+ minutes to get hot water. It's the same shower I mentioned in my first post with the flaky cartridge I can't get out or identify.

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                                      • #20
                                        I think we are on to something, it is possible, the re circulation pump is pulling cold water in to the hot water line through that shower faucet, you mentioned, this makes scene, it explains the cool water at the bottom of the water heater.
                                        I answer all plumbing and heating questions, all day long.

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                                        • #21
                                          I did want to come back and give you an update. I had to cut out the valve in the shower and replace it. This meant cutting an access panel and removing 6 tiles. Lot of work, but now I have hot water, just takes it awhile to get there because i cut off the recirculator.

                                          As far as the recirculator goes, cutting it off has lowered my electric bill about $65 a month. I was advised to move the line to the cold water inlet on the water heater and let the water re-enter there. Does this make sense? I do I get hot water out?

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