53 Comments

  1. Mother

    Please come and play testing plumber at our place…please, please, please

    Reply

  2. I had an expansion tank installed with my new water heater, with-in 2 months my water bill trippled. My water meter was continously fluctuating, after several visits by the plummer it was determined the expansion tank was causing the problem. The plummer removed the tank and my water bill went to normal. Could this problem have been caused by a faulty Expansioon tank? Have you ever heard of a situation like this?

    Reply

    1. Unless the “problem” was a water leak, I don’t see how an expansion tank could cause a bill to increase at all. When an expansion tank fails, the bladder ruptures and the tank simply fills with water, but that doesn’t create any additional demand or water use. I’d be curious to know exactly what your plumber claimed the problem was. Now, if you had a pressure tank (which is different than an expansion tank) that was increasing the water pressure to the fixtures in your house, then yes – that will increase water usage because more water is flowing through your fixtures when they are open. Although that’s not normally a “faulty” pressure tank, but simply a need to adjust the pressure down so that you balance pressure with usage.

      Reply
  3. madeline

    Hi,

    my husband replaced the expansion tank and when we turn on the heat for the house, there is this noise that sound like a microwave is running. Is that normal? Will this noise go away.

    Thank you

    Reply

    1. I bet the tank is vibrating against your water heater. If you hold it in place, does the noise stop? If so, you can try securing it with a metal strap!

      Reply
  4. Mark

    I’m replacing a 40 gallon water heater with a 50 gallon. There is no expansion tank currently. I’ve bought the Watts plt-12 (4.5 gallon) expansion tank. Is this too big? Should I use the 2 gallon model? Thanks!

    Reply

    1. Hi, Mark. The bigger expansion tank that you got will work fine! Go ahead and install it. Let me know how it goes!

      Reply
  5. KenB

    Thanks, best blog on expansion tanks. However, I don’t agree with your “yoga ball theory” that sitting on it will yield a higher pressure. If that were true then filling my car tires with 35 psi, before I put them on my car would yield a much higher pressure – but I know that’s not true.

    Reply

    1. Hi, Ken. Thanks for your comment! You’re forgetting about sidewalls on your car tires, which are rigid and help support downward pressure and keep the shape of the tire intact, and therefore the volume of the air cavity in the tire more constant. A yoga ball has no sidewalls. Nor does a balloon, which is why you can easily pop a balloon by sitting on it (decreasing the volume and increasing the pressure to the point of rupture). Google “Boyle’s Law” for a discussion of how volume changes affect the pressure of gasses (like air). Or, you can test emperically. Your pressure gauge when testing your expansion tank will read higher when your house’s water pressure is squeezing the air bladder in the tank vs. if you close the feed valve and relieve the water pressure briefly via the TPR valve or the drain. A proper pre-charge pressure will make this change more noticeable. If set too high, it would prevent water from entering the tank. Give it a shot and see!

      Reply
  6. Elly

    Hi Steve,
    My husband replaced our old expansion tank to a new one 2 days ago due to leaking. The water was hot but got warm after about 10 minutes right after he replaced the tank. However since yesterday there was no hot water at all. When he shut off the expansion tank and run the hot water, we get hot water but when he turned it back on we get cold water. Also the sound of the circulator pump was loud when he turned on the tank . We couldn’t figure out what’s the problem. Do you know what happened? Please help, thanks!

    Reply

    1. Probably air in the system. Bleed it out by opening all your hot faucets one at a time until they flow without sputter. That should do the trick!

      Reply

      1. Steve, the plumber who installed and removed my exspansion told me the water pressure on the bladder in the tank was expanding and deflating causing the water pressure in the line fluctuate with forward and reverse pressure to cause the water meter to spin forward and backward. The meter at the main turnoff valve was in fact spinning forward and backwards causing the meter to record a constant use of water. Once removed the meter immediately registered the correct use of water. Regardless of what the purpose of installing a pressure tank. I believe it’s a ploy to make money for the water company thereby making money for the city. We have been using water heaters for 70+ years and never had a problem. This is my belief.

        Reply

        1. Hi, Sam! Thanks for your comment. Your problem can be easily fixed with a check valve. I’ve got a swing check valve on my 1 inch line just “upstream” from the main water shutoff into the house, which prevents water from flowing back toward the street (and the meter). A check valve costs less than $5, and can be installed in less than 15 minutes. If that solution didn’t occur to your plumber in about 2.4 seconds, then you need to find yourself a better plumber. :)

          The only way your expansion tank would be able to generate enough pressure to push water back up your main and out to the meter is if your pre-charge was set WAY above your “normal” pressure, and/or your “normal” pressure from the street is extremely low.

          Again, I think your plumber is steering your wrong.

          Reply
      2. Elly

        Hi Steve, thanks for your prompt reply. I really appreciate it. I opened the hot water faucets one at a time this morning, but the water was still cold. My husband checked the pressure of the tank and it matched our water pressure (20 psi). He thinks the problem could be the circulator pump. Because if we shut off the pump, we get hot water but if we turn on the pump we get cold water. We never had this problem before until the old expansion tank leaked and we changed the tank. Please let me know your opinion on this.
        Thanks so much for your help Steve!

        Reply

        1. First, 20psi is extremely low for residential water pressure. If you’re on a well, you should look into increasing your pump pressure. If on city water, call and complain. You should be above 40psi, ideally at around 60psi. At that low pressure, it’s possible your recirc pump is pushing harder than your base water pressure! Check to make sure that the recirc pump is pumping in the right direction (pulling from the house and pushing toward the tank). You should have a check valve between the recirc pump and the tank, to ensure water only flows the correct way. Make sure you don’t have any check valves on the cold side between the water tank and the expansion tank, but you can (and probably should) have one on the cold water feed right as it comes out of the wall. Order of components from the wall to the tank on the cold side should be: check valve, shut-off valve, expansion tank, hot water tank. Also, are you checking your expansion tank pressure with the water shut off and pressure drained from the hot tank?

          Reply
  7. Skneuvean@sbcglobal.net

    All of a sudden tonight my potable water expansion tank is rattling/vibrating every two minutes then it stops after about ten seconds. What is going on and how do I make it stop?

    Reply

    1. Have you shut off the cold feed to the water heater, relieved the pressure, and checked the pre-charge pressure on the tank?

      Reply
      1. Shelley

        No and not sure I know how. Anyway to just disengage it until I get a plumber here?

        Reply

        1. Yes – this article explains how to shut off the water coming into your tank and check the pressure. Follow those steps to see if your tank has possibly failed.

          Reply
  8. Greg

    Greetings. My house is 16 years old. I had the original gas water heater tank replaced about one year ago. It is 75 gal. due to a spa bath tub. I did not have the original expansion tank replaced because the plumber stated it still worked (by releasing air from the stem). I don’t know if they messed with the pressure when they replaced the WH. One year later, periodically there are vibrations coming from the pipes just above the expansion tank. This has occurred in the middle of the night when no water has been run for several hours. It lasts for about ten minutes then goes away. What to you think? Many thanks in advance.

    Reply

    1. Do you have a pressure gauge on the system? I’d be interested to see if those noises correlate to increased pressure. If so, then I’d guess your pressure is set wrong in the tank. And the pressure was probably never set right by the plumber… they almost never are. :)

      Reply

  9. Josh

    Thank you great explanation. I am replacing my water heater and had a few questions about the expansion tank which you answered.

    Reply
  10. Stewart

    Steve: thank you for the brilliant details and information. In your photo titled “Partially drain your water heater to relieve water pressure” above, there is a white hose end which seems to lead to an in ground drain. What is that? I ask because my water heater in the recently purchased house has a solid pipe with an open end to the floor, but the drain is 3 ft away so the previous owner had a small bucket under the exposed pipe end which occasionally releases water into the bucket which I then check and drain as needed. I thought perhaps the expansion tank was shot but the knuckle test clearly seems to indicate that the upper portion is filled with water and the lower half of the tank has air (though the expansion tank sits vertically above the water heater with the pipe connecting from the bottom. Thank you for your time and kind assistance.

    Reply
  11. Rob

    Wow! I work in industrial maintenance. I at times write “How to” on the job. This is by far one of the most comprehensive DIY explanations I have seen on the internet, ever. It is how I try to make any set of instructions I put out. I am very familiar with thermal expansion and the tanks used to address the issue. Clear and informative with lots of pictures…….great.

    Reply
  12. bill

    if my expansion tank is bad,and I check my water pressure at the water heater like you’ve shown,wont that pressure reading include existing”thermal expansion”? I would think that is not the reading I would want to set my new tank pressure too. What am I missing?

    Reply

    1. If it’s bad, the tank will actually leak water from the valve (assume the valve is pointed down when you test it… and ideally, it should be). Once you’ve determined the tank isn’t leaking water (meaning it’s almost certainly good), just follow the steps in this article to test: shut off the flow into the tank, relieve some pressure from the tank with a partial drain, and then test the pre-charge pressure on the tank! :)

      Reply
  13. Kiley Ferons

    We just replaced the expansion tank, but when we went to test the water pressure from the drain valve on the water tank, no water is coming out. We have water running in the house and everything else seems fine, but not sure how to test the water pressure if nothing is coming out of the drain valve on the water tank.

    Reply

    1. Hi, Kiley. You can test your water pressure from any faucet attached to your house (including an outdoor hose-bib) with that pressure gauge. However, as you probably suspect, you may have something blocking your drain valve on your water heater.

      If you put a bucket under the water heater drain and open the drain valve, nothing is coming out?

      Reply
      1. Kiley Ferons

        The relief valve when flipped on does release water. But the drain faucet does not release more than a hot trickle.

        Reply

        1. Then yes – something is clogging your drain valve. If it hasn’t been flushed in a while (see my post on flushing water heaters), sediment and gunk can do that.

          On a day when you have the time to do so, try clearing the blockage by: 1) turn the gas to pilot, 2) attach a drain hose to your drain valve, 3) shut off the cold water inlet valve, 4) open a hot water faucet somewhere on the system to prevent vacuum, 5) turn off your recirc pump (if you have one), 6) open the drain valve (even if it’s just a trickle), 7) open the relief valve all the way until the water in the tank drops to the point where it doesn’t drain from it any more, then close the relief valve, 8) wait a while until the tank drains — if you can wait a few hours, that’s great, 9) open the cold water inlet valve in short bursts to see if you can swish water around in the bottom and clear the blockage.

          Another idea is that if you can turn the gas valve to pilot and wait long enough for the water in the tank to cool (overnight is preferable), attach a hose to the drain valve, open the valve, and blow in the other end of the hose (a short hose works best). You might be able to blow the sediment back into the tank, where it will disperse and drain easier. But be VERY careful with this method. Make sure the water has cooled off, of you’ll burn yourself! :)

          Reply
  14. Bret

    I recently replace the water pressure tank on my rural water system in the house, (the old ones bladder had failed). Now the pressure is more consant however i have noticed that when the hot water is on it wil get to a certain point the water flow will stop completly, wait a few seconds and then it starts again with now problems. I’m guessing this has something to do with the start stop pressures on the swtich, but not understanding completely what to next.

    thanks

    Reply
  15. Kevin

    This was an awesome guide! Thanks for taking the time to share your knowledge! I have an eighty gallon tank with an expansion tank size of 2.1 gallons. Should this be replaced with a larger tank? The house is new and still under warranty. Any help appreciated. Thanks again.

    Reply

    1. When it comes time to replace your tank, I’d go ahead and put the bigger one in. Probably no need to swap it out right away.

      Reply

  16. Steve, Thanks for posting this, it has GREAT information!

    We just bought a new house, and in the morning or after work, when I first turn on a water faucet I get a big rush of water for a fraction of a second. I also noticed that the water heater’s pressure relief valve is dripping most of the time. This lead me to get a pressure gauge, and do some testing. I found that when we come back from work the pressure is 150PSI!! As soon as we turn on a faucet for even a few seconds, the pressure drops back down to about 45-50PSI. This is a clear indication that we have a check valve and the expansion tank has failed.

    This has actually resulted in our water heater dying and needing to be replaced, since it isn’t supposed to be sitting at 150PSI all day, so this very simple check could save people HUNDREDS in repairs if they don’t!!

    Reply
  17. Theresa

    Thank you very much for the clear details! We are getting ready to buy a new water heater, a 40 gallon gas water heater (not sure what to buy yet!) The plumber says, we do not need an expansion tank. I thought all water heaters do need an expansion tank. He said there was something that my previous installation had that should suffice in place of an expansion tank! Not sure what that might be! Do you know what he is referring to? Thanks! Theresa

    Reply

    1. Hmm… I’d be very interested to know what he says is taking the place of the expansion tank. It’s very cheap insurance against major plumbing damage, and I can’t think of anything off-hand that can truly taking its place.

      Reply
  18. Theresa

    Additionally, there was no expansion tank when our previous one was installed about 10-12 years ago, a direct vent A.O.Smith. Thanks again!

    Reply
  19. Robert D

    Steve,

    Thank you for this comprehensive page! I have some questions for you: the TnP pipe on my hot water heater has been dripping since we’ve turned it on a couple of weeks ago. Additionally, our gas boiler is also dripping from the backflow pipe when both are running. The two lines where the leaks are occurring are connected directly and indirectly to one another. The cold lead into the hot water tank feels warm to the touch. The boiler has an expansion tank but the 40 gallon hot water heater does not. I think it could be one of two things. Either the backflow valve on the boiler needs to be replaced (what several people have told me) and/or there needs to be an additional expansion tank ( what I think as a layperson). The water pressure is within the expected range. I feel like installing an expansion tank would stop both leaks. Should each system (boiler/hot water) have their own expansion tank or would one work for both systems? I haven’t tested the pressure in the line expansion tank but i think it might be fine. Any thoughts on your end?

    Reply

    1. Hi, Robert. Backflow valves (or check valves, as I call them) do eventually go bad and should be inspected and replaced as needed. I’d start there with the boiler.

      Next, if your TnP valve is a few years old, it might just be time to replace it, as well.

      As for the cold water inlet on your hot water tank being warm to the touch, I had that same problem. I fixed it by putting a check valve on the cold water side of my water heater, but you need to make sure it’s installed “uptstream” of your expansion tank. If you also run a vacuum breaker valve in your setup (like I do), the check valve needs to be “downstream” of the vacuum breaker. Check this blog post (and pay particular attention to the last photo) to see how I have mine set up:

      http://www.stevejenkins.com/blog/2014/06/diy-sharkbite-fittings-make-adding-a-check-valve-easy/

      If your current expansion tank is installed so that no check valves exist in the plumbing between the water heater and the boiler, then one large expansion tank SHOULD be able to help absorb any temporary over-pressure issues on both.

      But if you have any check valves that could prevent any flow between the boiler and the tank, your safest bet is to throw a separate expansion tank on the water heater. They are cheap insurance. :)

      Reply
  20. DHD

    If I follow your directions to check expansion tank pre charge and I see that it’s on the low side can I pump it up while it is still attached or must I remove it, charge it and then reinstall?

    Reply

    1. As long as you have the valve that lets water into the main hot water tank shut OFF (no there’s no water pressure hitting the expansion tank from the “upstream” side) and the main hot water tank is partially drained (so there’s no water pressure hitting the expansion tank from the “downstream” side), then you don’t need to remove the expansion tank to set the pre-charge pressure properly. There must be NO external pressure on the tank’s bladder from water pressure anywhere in the system while you set the pre-charge pressure.

      Reply
      1. DHD

        Followed your great directions for replacing the expansion tank, except I cannot get the old tank off. It’s been on for 12 years. I can get a good grip on it, easy access but it won’t budge. I’m afraid of damaging the pipe, etc. Any tips. Seems simple enough.

        Reply

        1. Try applying some heat to the thread location. Heat gun is preferable, but light torch if you have to.

          You might also try some type of anti-seize blasting spray (check your hardware store).

          If you’re lucky, the old tank might actually have a nut-shaped collar near the base of the threads, and you can use a wrench. Just be careful to hold onto any pipes that connect to it, so you don’t pull anything else loose.

          Reply
          1. DHD

            Thanks for the quick response. It does have a nut collar on it and I am able to get a good grip on it, it just won’t budge. I have not tried anti-seize. I did spray it last night with WD 40. Is anti seize that much different?


          2. It’s slightly different, but I think your best bet is heat. If you have a butane torch, hit it for a second or two and see if that makes the metal expand enough to let go.

  21. William

    Hi Steve.
    Thanks so much for sharing your knowledge. I was able to replace my pressure tank but still have rumbling and rattling sounds from the pipes. I cannot figure out were they are coming from. I tried draining but was not successful. Please advice me.
    Thanks
    William

    Reply

    1. Is it water hammer type rattling? You might want to check into a water hammer arrester. I installed two on my washing machine, and that fixed the last of the “popping” noises for me!

      Reply

  22. Hi there. I moved into my house in Aug 2014. First time having an expansion tank. It’s very loud. Sounds like a choo choo train. I don’t think it’s right. I posted a video on my fb profile. Has it failed? Sometimes it knocks really loud. Thank you.

    Reply

    1. Hi, Karen. I watched your video, and what strikes me is how rhythmic the sound is. You said in the caption of the video that it’s while your washing machine is running. Does it ever do this when the washing machine isn’t running? There’s a good chance it has failed. If you shut off that water valve and check the pressure of the tank with a tire pressure gauge, what does it read?

      Reply
  23. Paul Revis

    Steve, thank you for this tutorial. It was a big help when my tank failed this morning.

    Reply

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