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Thread: Did I Need An Expansion Tank?

  1. #1
    DIY Member BDP's Avatar
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    Default Did I Need An Expansion Tank?

    I try and research my plumbing issues before I call in the professionals just to be well educated, though am smart enough to know when not to DIY and call in pros like yourselves. However I am always wary of getting a fair shake with repairs so have a question.

    Have a standard tank water heater in my home, 11 years old now. Started to leak water at a fairly regular rate from the release valve pipe. Opened it to flush it out and closed it and leak was even faster now (about a gallon an hour) so decided the value was bad, called the plumber to replace the valve.

    Plumber got here, said at the minimum I needed both a new valve and an expansion tank. The expansion tank surprised me. He said without it, would just keep leaking even with a new valve. Also tried to sell me a brand new tankless water heater or high end heater at a pretty high price (which I won't get into here, I know we don't talk prices). The parts and labor on the tank and valve was also higher than expected.

    At any rate, can anyone at least tell me if this is normal, to add an expansion tank to a standard water heater of this age when valve leakage happens? I can't take it back now, obviously, but I'd like to know for the future when dealing with this company. I guess I just didn't like the concept of trying to be sold a brand new unit when it was just the valve leaking and I knew that.

    Thanks for any advice as always. If anyone wants to PM me I can give you the prices I paid/was quoted perhaps.

    Thanks,

    B.

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    The answer is dependent on local codes and/or whether or not you have a closed plumbing system.

  3. #3
    DIY Member BDP's Avatar
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    Not sure on the local codes, but I guess my system is open...I have city water/sewer. Not my own well or anything. If that's what that means.

    I just got a little shaky at the fact that he said just putting the new valve on would leak again, that without the expansion tank the new valve would just eventually leak. And even with the tank, he told me I'm on borrowed time, which felt more like he was just trying to really sell me a complete new unit.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    A well would NOT normally need an expansion tank. If you have a city water system and have either a pressure regulating valve or check valve in the line to the house or water heater, then you DO have a closed system and SHOULD have an expansion tank, (although there are thousands of houses that do not have the tank even if they should). Under any other situation, you do not NEED an expansion tank, and having one would not give you any benefits.

  5. #5
    Nuclear Engineer nukeman's Avatar
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    What is meant by closed/open system is whether there is a check valve (1-way) on the supply. This could be at the meter itself or if you had a pressure reducing valve, that would cause a 'closed' system as well. If there is a check valve, the pressure builds in the system as the water expands while being heated in the water heater (nowhere to go). The pressure can build to the point where the relief valve opens a bit to drop the pressure. If you have an expansion tank, the expanded water has a place to go and keeps the pressure in check.

    If your system is open, then water can be pushed back to the street if the pressure goes above supply pressure.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    At that age, it would not be unusual for the T&P valve to leak. If it hadn't been regulary checked, and you manually opened it, leaking after that is pretty common; the rod often has a buildup of crud on it, and won't go all the way back in to allow it to seal plus the rubber seals themselves are probably worn out.

    At 11-years, the WH is probably on its last legs. It could die tomorrow, or last another 20-years, but 11-years is in old age territory - most die earlier. That valve is designed to release water if the pressure exceeds 150psi or the temp gets too high. So, you need to eliminate over temp as a cause. You can buy a peak reading pressure gauge at a big box store for about $10. You could screw it into say your washing machine supply or the drain on the WH and leave it for a day or so. Look at the static pressure, then let it sit there for a day or so and see how high it ever gets. If the pressure is 'normal' when using hot water, but when you finish say a long hot shower, it slowly rises, you probably have a closed system and need the expansion tank to solve the problem. 'Normal' is below 80psi. If it is above that without thermal expansion, then a PRV is called for and then you certainly would need an expansion tank. If you have a PRV or an expansion tank, they may be shot.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    In the trades Dana's Avatar
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    What jadnashua said.

    T & P valves DO go bad, and replacing them isn't a rocket-science DIY project. If your static pressure is high (you should measure it) the water-hammer effect from solenoid-operated valves in washer/dishwashers can get the things to spit sometimes, but that's not likely to be a steady gallon-per-hour kind of thing. The T & P valve is toast. If it was fine for the first 10 out of 11 years of life and your measured water pressure is reasonable, that's likely to be all you need until the tank really craps out.

    In MA check-valves are required to have a 1/8" hole to allow for thermal expansion, but if there's a pressure reducing valve on the line an expansion tank is still a good idea if you have 10s of gallons of water heater volume. (Tankless heaters & heat exchanger coils in boilers/buffers are very low volume.)

  8. #8
    DIY Member BDP's Avatar
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    As always I do appreciate the vast amount of knowledge and the responses here. You have made me feel better about the install. It sounds like, given the fact that my local water company has raised pressure, and that I don't have a PRV on my main water line into the house (not yet anyway), the expansion tank was a good idea. I guess the final cost just was more than I expected given I thought I would just get a new valve and nothing more. Had I known the cost I was looking at I'd have called some of the big boxes about putting in a whole new water heater. I'll probably still price it out knowing my unit is 11 years old.

    By the way, are the gas water heaters with the blower unit on top more expensive than standard electric models? I assume so. Also, if I have one of these type, do I need to replace it with the same type? I don't really want to spend the bucks for tankless or anything fancy, I'm fine with the tank though I think it will need to be gas. I only plan to be in this home a few more years but I want to be prepared in case it does totally fail on me.

    Again thanks for all the advice. It looks like the valve was black and in bad shape when he took it out so that was the root cause. I probably should have tried to do the valve myself though looking at the bill for this!

  9. #9
    Plumber Cass's Avatar
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    If you did not have a PRV or check valve then the plumber did not know what he was doing...the expansion tank is useless under those conditions...

  10. #10
    DIY Member BDP's Avatar
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    I might have a check valve, not sure on that...My home is around 10 years old, not sure if a check valve was standard but I would assume I at least have that. I don't have a PRV at the main line at this point though I know a lot of folks in the area are getting them due to the water company jacking up the pressure. Think I measured in at 85 PSI at the outdoor hose line when he checked. But he wanted another $325 to install the PRV and that was just too much for the visit in addition to what I already had done.

    So you are saying without the PRV the expansion tank was useless? Hmmm.

  11. #11
    In the Trades Gary Swart's Avatar
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    It is becoming more common for new water meters to have a check valve to prevent cross contamination of their water mains. I'm not sure how real the danger is of that, but that's for another discussion. I doubt if you have that kind of meter due to the age of your house. To make it even more confusing, some pressure regulating valves have a bypass for expansion! No worries for you at this point. One problem with high water pressure is the stress it places on valves, especially in toilets and washing machines. While there is no exact maximum or minimum pressure for homes, "normal" pressure ranges from a low of perhaps 40 psi up to 80 psi. Personally, I have mine set at 50 psi and find it to be plenty for me. My outside hose bibs are not pressure regulated, so have the full 90 psi provided by the city. My suggestion to you is to install a PRV and an expansion tank. I'd set the pressure at about 60-65 psi at both the RRV and expansion tank. You can always increase or decease the settings, but remember the expansion tank air charge has to closely match the PRV setting.

  12. #12
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you have a check valve and your static pressure is 85, the system pressure often increases, sometimes radically, overnight when people stop using water you probably need an expansion tank . Even without high static pressure, depending on the size of the WH and how much you drain it, there is likely enough expansion to require an expansion tank. The only thing that will regulate that in house for you is a prv with an expansion tank. As noted earlier, spend the $10 or so to buy a gauge, and leave it connected for at least 24-hours or so to see what your peak pressure is (make sure to get one with the 'tattle-tail' hand so it shows peak pressure). Then, instead of guessing, you'll know. Then, you can plan on the best course of action to resolve the problem. If the T&P is releasing, it is either bad, or is doing its job. If the temperature was excessive, you'd probably know it. You might not if the pressure was excessive since it may not be constant and often peaks in the middle of the night.

    Again, if you have a closed system (check valve or prv), you need an expansion tank. If your supply pressure is excessive, having a bypass may not solve your problem. A bypass in a prv only works if the pressure inside of the house is greater than that in the supply. If your supply is very high, the T&P will still trip since it may be lower than the supply pressure set point. Normally that isn't true, but those pressure swings aren't good for the plumbing...things last longer with a more constant pressure.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  13. #13
    DIY Member BDP's Avatar
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    Thanks. So it sounds like I am most of the way there. Yesterday, he put in a new release valve at the water heater, and an expansion tank. I still do not have a pressure regulator on the main line coming into the house. Sounds like I need that too if I really want to do the right thing. In the end, I probably should have had everything ripped out and started from scratch. I think the pressure regulator on the main line into the house was free if I bought a new system from them at their inflated prices. For now, all I got was the new valve on the tank, and the new expansion tank.

  14. #14
    Plumber Cass's Avatar
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    since he is not supposed to set the tanks air pressure above 80 PSI...I wonder what he did...he should have shown you the check valve if you had one because that would have been the only reason to install one...it is located where the water enters the home...they have gone away from ckeck valves in the meters because they start making noise after a few years and that causes a service call for the utility...something they don't want...because they own the meter
    Last edited by Cass; 02-16-2010 at 07:35 AM.

  15. #15
    DIY Member BDP's Avatar
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    Is there any way I can tell looking at the tank? Probably not right? I don't see a way to read air pressure where he's got the little tank, it's just mainlined in above my old existing tank.

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