hot water cools fast

Discussion in 'Plumbing Forum' started by ilyaz, Mar 6, 2010.

  1. Mar 6, 2010 #1

    ilyaz

    ilyaz

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    I recently noticed a weird trend: when I turn on the shower, it is hot first but then water starts dropping in temperature pretty quickly so that every 30 seconds or so I need to adjust the shower to raise the temperature. This started happening a few days ago -- about the time we started our kitchen remodeling when we demolished everything and, among other things, disconnected the old sink and the dishwasher. I am wondering if this has something to do with the problem. By the way, it has never happened before, i.e. unless several people were taking a shower before me for extended periods of time, temperature would not drop at all. Also, I tried raising the temp setting on the boiler. This gave the expected result: while the water would be hotter initially, it would steel get cooler. The same thing happens in all two of the three showers we have in the house, and we don't use the 3rd one. What's happening? Thanks much!
     
  2. Mar 6, 2010 #2

    Nestor_Kelebay

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    Don't do your testing in the shower. Tub & Shower valves have "anti-scald" features on them that cause a decrease in the flow rate of the hot water if there's a pressure drop in the cold water supply and vice versa. So, the problem may be originating with the anti-scald feature on each of your shower valves, and despite the fact that it's unlikely that both shower valves will have the same problem, it just introduces another variable into the analysis.

    Test the water temperature on a bathroom, kitchen or laundry room sink and see if the same thing happens. If so, then read on...

    There's a good chance the "dip tube" inside your water heater is broken or cracked.

    If you notice, both the cold water inlet and hot water outlet are located at the top of your water heater. To prevent that incoming cold water from being sucked into the hot water outlet, hot water heaters are equipped with a dip tube. You see, cold water will only come into the hot water heater when there's hot water being drawn off at a faucet, and so something must be done to prevent the cold incoming water from taking a shortcut by going directly to the hot water outlet and cooling down that hot water down. That something is the "dip tube".

    [​IMG]

    That dip tube ensures that the cold incoming water is far enough away from the outlet of the water heater that the greater density of the cold water prevents it from simply being sucked into the hot water outlet.

    You probably have a broken dip tube. The way to check is to run the water at the closest faucet to the hot water heater until it's running as cool as it gets. Now, shut the cold water supply valve to the hot water heater, open a hot water faucet on the the top floor of your house and the drain valve on the hot water heater to allow water to drain out of the hot water heater. Feel the water coming out. If the water coming out that drain is hotter than it was coming out of the faucet, then it's clear that you're not getting all the hot water out of your water heater, and that's typically because cold incoming water is being sucked into the hot water outlet, and that's what your dip tube is meant to prevent. So, your dip tube is prolly broken or cracked or busted or on strike or just plain fed up or something.

    This is a fairly common problem with hot water heaters.

    Remember to close the heater's drain valve, shut the hot water faucet, open the cold water supply valve to the heater and bleed the air out of your house's hot water supply lines by opening the hot water valves in your house to release any trapped air.

    I've never replaced a dip tube on a hot water heater. I've been told that the anode rods can be very tight and difficult to remove, but I don't know if the same is true for dip tubes.
     
    Last edited: Mar 6, 2010
  3. Mar 6, 2010 #3

    Redwood

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    Okay you say boiler do you heat the domestic hot water with a tankless coil or, have you got an indirect water heater?
     
  4. Mar 6, 2010 #4

    ilyaz

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    The heater is Whirlpool model # BFG2J5040T3NOV

    This site: Whirlpool Water Heaters states that it has a 12 year warranty, and it's only a few years old (definitely less than 12, I don't remember when we installed it but it has ANS number ending with 2004, if it means anything). Could this be covered by the warranty?
     
  5. Mar 6, 2010 #5

    Nestor_Kelebay

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    Ilyaz:
    That's a question that you'll have to ask Whirlpool. The web site you linked to has a phone number at the bottom, and I'd start there. Or, download the Product Manual for your water heater and see exactly what the warranty covers. The warranty shouldn't be hard to find in the product manual.

    Typically, the lifespan of a hot water heater is determined by the enamel coated tank inside it. Once that enamel coated tank starts to leak, that's the end of the water heater. So, I suspect that the 12 year number applies primarily to that tank.
    The only thing you can do is find out.

    If the dip tube is covered, you might want to talk to the plumbers that will be doing the work and pay extra to have them pull out the anode rod and check to see what condition it's in, and possibly replace it. Check with Whirlpool that this doesn't affect your warranty. I expect as long as you replace your old anode rod with a genuine Whirlpool replacement anode rod, it shouldn't. The anode rod's job is to protect the steel wall of the enamel coated tank by corroding instead of the steel tank. So, as long as the anode rod has lots of aluminum or magnesium on it, the steel tank is protected against corrosion. It's when there's no aluminum or magnesium left on the anode rod that there's no more cathodic protection of the steel tank, and the steel tank will corrode at it's normal rate. So, if you pull the anode rod, and you see that there's not much left of it, then I'd pay to replace that anode rod. And, I expect I'd do that even if it voids my warranty because in that situation, I'd be more confident in the new anode rod to protect my steel tank than I would in the warranty to do that.

    They use exactly the same principle on galvanized metal and galvanized nails to protect the underlying steel from corrosion. However, they don't use zinc for anode rods because zinc is a natural biocide (poison) like copper, and you don't want to be drinking zinc ions if you can avoid it. Magnesium ions, on the other hand are something we drink every day without getting sick. Even soft water will still have some magnesium ions in it.
     
    Last edited: Mar 6, 2010
  6. Mar 6, 2010 #6

    ilyaz

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    I called Whirlpool. They asked me whether I ever drained and flushed the water heater, which I never did. The heater was installed in 2007. I have two questions:
    1. Could this be the cause if the dropping temperature?
    2. I looked in the manual for instructions on how to drain and flush. It requires turning gas off and then turning it back on. Since I've never done it, I am a bit nervous. I can call a plumber, of course. But is it possible to flush and drain without turning the gas off?
     
  7. Mar 6, 2010 #7

    kok328

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    I have the same problem with my water heater but, really don't care to tear it apart to replace the dip tube unless, it gets to a point where I can't get a full shower out of it.
    The standard instructions for draining and flushing a water heater are somewhat inadequate. Best practice is to completely remove the drain valve due to pieces of sediment (calcium) being larger than the drain valve, it clogs up the flow of water and restricts smaller pieces of sediment. Poke around with a piece of coat hanger to help pieces past the the drain valve opening. Repeat the procedure a few times until it appears everything is out. Filter to the water being drained to get an idea of how much calcium is being removed. A sure sign that your heater has sediment, is that it will sound like tumbling rocks or popcorn popping when heating up.
    You can perform this procedure without totally shutting off the gas but, at least set the thermostat to it's lowest setting. On an electric water heater, they must be shut off completely.
     
  8. Mar 6, 2010 #8

    ilyaz

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    So am I to do this:
    1. Shut off cold water to the tank
    2. Turn the temp dial to VACATION or whatever the lowest setting is
    3. Drain tank from the drain valve
    4. Remove the valve, poke with coat hanger
    5. Replace the valve
    6. Turn on cold water
    7. After it fills, go to step 3 and repeat steps 3-7 a couple of times or at least I don't hear popping while draining
    8. Set temp to normal

    Thanks!
     
  9. Mar 6, 2010 #9

    Nestor_Kelebay

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    Ilyaz:

    Flushing the hot water heater is generally good preventative maintenance, but it won't fix your dip tube. Every hot water heater manufacturer recommends that it's customers flush their water heaters once a month just to remove dirt and scale from the heater. However, flushing your heater will not affect the hot water cooling down problem your first post was about.

    The standard procedure for "flushing" a hot water heater is as simple as mud, and it goes as follows:

    1. Simply open the drain valve of the water heater until the water runs clear.
    2. Close the heater's drain valve.
    3. Repeat Steps 1 and 2 once a month.

    While Kok may be right that if you take the drain valve off, you can get into the heater with a wire and break up any lime or scale inside it, A. O. Smith makes an "Un-lime" kit to do that. Basically, it's a gallon jug of a mild acid that you connect the to the drain valve of your water heater.

    The instructions for using the Un-lime kit can be found here:

    http://www.hotwater.com/lit/training/4800r9.pdf

    Basically, the procedure is to:

    A. Drain the water out of the hot water heater:
    1. Turn the temperature control down to "Vacation"
    2. Close the cold water inlet valve to your water heater.
    3. Open a hot water faucet and the drain valve on the heater to allow the heater to drain

    B. Use the Un-Lime kit:
    4. Connect the hose from the Un-lime kit from the heater's drain valve to the gallon jug of mild acid.
    5. Elevate the jug of acid so that it flows into the water heater, and leave it in there for 1 minute
    6. Lower the jug of acid so that the acid flows out of the heater and back into the jug.
    7. Repeat Steps 5 and 6 until the acid flowing back into the jug doesn't have any foam in it anymore. (That foam is CO2 gas, and it's the result of the acid dissolving calcium carbonate (which is lime scale) inside the water heater.)

    C. Put the water heater back into operation:
    8. Once there's no more foam in the acid, remove the Un-lime kit from the water heater, open the water supply valve to the water heater for a few seconds to flush out the spent acid. Then, close the drain valve and the hot water faucet. Open the water supply valve to the heater. Turn the thermostat back up, and bleed the air out of the hot water supply pipes.

    D. Properly dispose of the spent acid
    9. Wait until it gets dark, and go throw the spent jug of acid in your local river or lake.

    The acid won't harm your drain valve or the tank. It only dissolves any lime scale you have inside the tank. You can contact A. O. Smith tech support in you want to know more about purchasing and using one of their Un-lime kits.

    Removing the lime from your water heater will extend it's life because the lime will insulate the water from the source of the heat, and that causes the bottom of the heater to get hotter than it otherwise would. Removing the lime ensures that the bottom steel wall of the tank doesn't get any hotter than it should.

    However, this is all fine and good, but you need to replace your dip tube to solve the problem.
     
    Last edited: Mar 6, 2010
  10. Mar 6, 2010 #10

    Redwood

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    Oh Boy! Here we go again....:rolleyes:

    Ilyaz I doubt your problem is a sediment build up unless your water is extremely hard. Are you hearing any popping noises while the burner is on reheating the water in the tank after use?

    I would simply follow the manufacturers flushing instructions and no you cannot do it without turning off the burner. Dry firing the water heater when empty will damage the water heater.

    1. Is the burner firing properly after water use to reheat the water?
    2. Is the water coming out of the water hot enough? Measure the temp with a thermometer.
    3. Do you have a tempering valve installed after the water heater.
    4. Is there any possibility of hot water leaking with or without your knowledge? Are you on a slab foundation?

    American Water Heaters has had some problems with thermocouples as well as the Robert Shaw gas valves as well, but a few answers to the questions above would help.

    The diptube highly detailed by Nestor is unlikely unless your water heater was incorrectly installed and the plumber burned off the dip tube soldering too close to it or, the water heater was manufactured between 1992 and 1998.
     
  11. Mar 6, 2010 #11

    ilyaz

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    Redwood, I may be misreading your post, but I am confused: are you saying that the reason for the drop in temp is not the diptube and it's not a sediment build up either, but you still suggest draining and flushing? So what is the reason for the temp drop? And what would be the advantage of draining and flushing?

    By the way, here's another piece of info. Our utility sink is next to the heater and its faucet does not have any volume control so I can turn the water like it's the Niagara Falls. I noticed that when I do that and it's hot water, the water gets cloudy. Is this the buildup?

    Thanks.
     
  12. Mar 7, 2010 #12

    Redwood

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    Yes I sincerely doubt your problem is either sediment or, a bad diptube.

    The cloudiness of the hot water you just described is simply air in the water.
    If you run the water into a glass the milkiness will clear from the bottom up to the top of the glass fairly quickly.

    The most important thing right now that you could tell me is is the water good and hot at the utility sink right next to the water heater?

    Does it stay that way for a while?
     
  13. Mar 7, 2010 #13

    ilyaz

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    Yes, it seems to stay hot somewhat longer than in the shower.
     
  14. Mar 7, 2010 #14

    Redwood

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    That pretty much rules out the water heater not working right, leaks, and a tempering valve problem.

    Do you have any single handle faucets in the mix?
    Moen and Mixet have a notoriety for hot cold crossover problems...

    Are there any fixtures where the hot and cold can be turned on with the water turned off at the outlet?

    Or, a Y connection being used on a washing machine...
     
  15. Mar 7, 2010 #15

    ilyaz

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    No Y's
    The only single-handle faucet was in the kitchen but it's not there anymore, just two pipes sticking out from the floor.

    Not sure I understand you 3rd question. Can you give me an example?

    By the way, what happens if the heater is never flushed/drained? We've had it for about 3 yrs and never performed any sort of maintenance on it.
     
  16. Mar 7, 2010 #16

    Nestor_Kelebay

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    I don't want to hijack this thread. I'm interested in Redwood's analysis of what's causing a gradual and steady cooling of the hot water in the shower (besides a bad dip tube). And, I could think of an example of the kind Ilyaz wanted, so I figured I'd speak up.

    An example might be a shower head that allows you to turn off the water at the shower head temporarily to lather up. If someone were to do that, (to answer the phone, say) and then dried off and got dressed and never did shut off the water at the faucet, then there would be a direct connection between the hot and cold water supply piping via the shower valve. If that person then came home and turned on the lawn sprinkler, he could find that he's watering his lawn with hot water instead of cold water. In Plumber-ese, that kind of situation is called a "cross connection".

    What Redwood is thinking is that you might have one of these cross connections in your house, and any cold water getting into the hot water supply piping would result in the shower gradually becoming cooler. (cuz then you have cold water coming in both the cold water and hot water supply piping into your shower valve)

    What happens if you don't flush your water heater for three years?

    That depends heavily on the hardness of your water.

    Scale, or "lime" forms on the hottest surfaces when water is heated. This scale is formed from the hardness ions in the water precipitating out on hot surfaces. So, if you have hard water and you have a gas fired water heater, you can expect a lot of scale to form on the hot bottom of the enamel coated tank where the gas flame impinges. That scale insulates the water from the flame, and causes the metal bottom of the tank to get much hotter than it otherwise would, and that will increase the thermal shocking to the tank and shorten the life of the tank.

    The same thing happens on the heating elements of an electric hot water heater. However, in that case, the heater can be drained and the heating elements removed and cleaned.

    If you have soft water, then you get much less scale because most of the hardness ions have been taken out of the water before it reaches your house.

    If you have soft water, you probably didn't do any harm at all to your water heater by not flushing it for 3 years. Truth be told, lotsa new home owners never flush their water heater. I had an A. O. Smith BTRC250 commercial water heater, and every time I'd flush it, the water would run clear right off the bat, so I eventually stopped bothering to flush it every month. The whole idea of flushing is to clean out any sediment or dirt accumulated at the bottom of the tank, but in my case, there was never any accumulated dirt to flush out.

    If you do have any scale forming in your water heater, the tell tale sign is that your water heater will make funny (rumbling, popping or wheezing) noises when the main burner trays are firing. If you don't hear any funny noises like that when your water heater's main burner trays are firing, then I wouldn't be concerned.

    Just start flushing your water heater every month from now on.
     
    Last edited: Mar 8, 2010
  17. Mar 8, 2010 #17

    Redwood

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    Flushing the water heater is a good idea and you should do it but I don't think it's your problem.

    No single handle lav faucets or, tub/shower mixers?
     
  18. Mar 8, 2010 #18

    ilyaz

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    I don't think so, but just in case, I am attaching pix of all of my faucets and showers.

    all2.jpg
     
  19. Mar 8, 2010 #19

    Redwood

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    The lav faucet in the upper left is a Moen.
    Try shutting off the stop valves under the sink and see if the shower improves.

    There is also one on the center right that is a single handle for a tub/shower but the pic is not clear enough to see the brand.

    Try it with that one lav faucet shut off underneath the sink.
     
  20. Mar 8, 2010 #20

    ilyaz

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    Will do

    This is also a Moen. By the way, this is a replacement installed a few months ago in place of the previous one which was at least 10 yrs old and whose cartridge went bad. What we have noticed is that water pressure in the new one is lower than in the old one. My wife is complaining that there is not enough pressure for her to take a normal shower. Can this be related somehow to the temperature problem?

    Thanks much!
     

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