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Thread: Did I Need An Expansion Tank?

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  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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    Default

    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
    Important note - I'm not a pro
    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.)

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