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We live in an apartment and do rent but we are only getting lukewarm water it will not get above about 90 to 95 degrees Fahrenheit. Our maintenance man has been over here trying to figure it out but no such luck. For some reason when we turn off the cold water valve going directly into the hot water tank the water starts to heat up. But when we turn back on the cold water it stops working. I know the cold water will cause the rest of the water temperature to drop. But we've waited hours and for some reason it will still not heat up. They have changed out both the thermostats and heating elements but to no avail. If anyone has an answer that would be most helpful. Thank you and please help!

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    When you turn off the cold water valve, how can you tell if it's heating at that point?
    – rogerdpack
    Commented Sep 8, 2022 at 18:27

7 Answers 7

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I suspect the pipe that puts water into the tank, known as the dip tube, is broken inside. So when you use hot water, the cold water enters at the top, when it should enter at the bottom. This would be the case if by "heating up" you mean the temperature of the water coming out of your hot water taps.

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Like Tiger Guy said, the dip tube might be broken, but and here's the big BUT.... The hot and cold connections might be reversed. Normally this results in trapped air near the top of the tank, sometimes enough to expose the upper heating element, that's not at all good! but if your pressure is high enough, it might submerge the element. Do you hear any "whossing" sounds from the water heater when hot water is being used?

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  • My parents used to have a water heater that was mis-piped in this fashion. If one went long enough without using any hot water for awhile, the tank would heat up, and if one continuously used hot water it would stay hot, but if one stopped using hot water it would take forever to warm up again. Depending upon the layout of cold-water plumbing above the tank's intended outlet, I can imagine that convection might result in warm water flowing up one side of that pipe, cooling off in the uninsulated pipes, and flowing back the other side. This could prevent the tank from ever getting very hot.
    – supercat
    Commented Sep 9, 2022 at 17:56
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Another possibility is that you have a leak. When you have a big enough leak, the water never has a chance to heat up. Instead, the warm water leaks out and is replaced by cold.

In that scenario, turning off the cold water stops pushing the water out of the hot water heater to the leak. So the water in the tank heats up. Then you turn the water on again and you can get hot water. But if you turn off the faucet or shower, the remaining hot water leaks out and you're back to never fully heating the water in the tank.

You can tell if you have a leak by turning off all the faucets and checking the water meter. If the water meter shows flow with everything off, there's a leak. The next step would be finding the leak, which is worthy of its own question.

If you establish that there is not a leak, then you can reexamine the other possibilities.

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  • Sorry, but I have to disagree, it would have to be a very large leak if the water heater couldn't keep up to set point. It would be on all the time and their gas bill or electric bill would certainly be very high. Regarding checking the water meter: That only works if you have one. I'm on a well with no metering as are lots of other people.
    – George Anderson
    Commented Sep 9, 2022 at 12:18
  • @GeorgeAnderson Since they are in an apartment, there is a possibility that they are not metered individually.
    – evildemonic
    Commented Sep 9, 2022 at 14:07
  • @evildemonic Are saying electric and gas might not be metered individually? That would surprise me, but it's a possibility. All appts here are individually metered, not sure about water. At any rate, it would still take a heck of a leak to prevent the water heater from reaching setpoint. This is an interesting question. I hope the OP will tell us how it was resolved.
    – George Anderson
    Commented Sep 9, 2022 at 15:24
  • @GeorgeAnderson Yes, I've lived in apartment buildings where the building itself has a meter, but the individual units do not. Utilities were included in the rent. I do agree that the supposed leak would have to be extreme, so while a possibility, it is unlikely.
    – evildemonic
    Commented Sep 9, 2022 at 18:36
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Another possibility, although not likely, is that a bypass is open.

Sometimes in apartment or commercial buildings, a pipe and valve is installed to bypass the water heater so that water can run in the hot water taps while the heater is being swapped out.

A failed shower mixing valve can also act as an open bypass.

If the bypass is open, water will circulate through the heater even when the taps are closed, plus, the bypass will mix cold water with the hot when a tap is opened.

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Very simple problem to repair all hot water systems have a non return value fitted to the cold inlet at the bottom of the hwu clearly this valve no longer stops hot water from getting into the cold feed so if you turn on a cold tap it can draw the hot water out and than exess cold water refills the tank therefore making the hot water luke warm

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    I wouldn't go so far as to say all hot water systems have the cold water feed at the bottom. Mine doesn't.
    – FreeMan
    Commented Sep 10, 2022 at 15:35
  • I've never seen a water heater with a non return valve.
    – Hot Licks
    Commented Sep 10, 2022 at 23:40
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Conduct a tong test (current test) to ascertain if the element is drawing a current during your normal situation.

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    This could do with an edit to further describe exactly what a "tong test (current test)" is, how to perform it, and how to interpret the results in application to the situation at hand. It's always best to presume the person asking the question is not familiar with technical terms and procedures and to over explain rather than under explain.
    – FreeMan
    Commented Sep 9, 2022 at 12:03
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I'm thinking what could be the problem is that that the tankless water heater you have may not be big enough and the water pressure coming from the cold water supply is too high so you may have to install a pressure relief valve to slow down the water pressure going into your tankless water heater because then you take this water heater will have enough time to heat up the water try that first before anything else but also there could be a leak somewhere but I don't agree with that good luck

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    The OP states they have a water tank, not a tankless.
    – JACK
    Commented Jun 3 at 12:31

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