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Thread: Replacing expansion tank on waterheater?

  1. #1
    DIY Junior Member gabby's Avatar
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    Cool Replacing expansion tank on waterheater?

    Need to replace expansion tank on water heater. What do I need to do first besides cut valve off to expansion tank? The tank is full of water an laying over on its side. Any help will be appreciated.

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    In the Trades Gary Swart's Avatar
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    All you should have to do is turn off the water supply going to the expansion tank. The tank attaches to the water line with a screw adapter, so when you have the water off, you just unscrew the tank. Care, it will be heavy because it will be full of water. The new tank screws on the adapter and that's all there is to it except for making any pressure changes to the tank to match the PRV setting.

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    General Engineering Contractor ballvalve's Avatar
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    If its been full of water for along time and your T&P valve is not leaking, I would cut it off and throw it away forever.

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    DIYer, not in the trades LLigetfa's Avatar
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    Full may be a relative term. Perhaps it's 90% full and the remaining 10% is saving the day.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Quote Originally Posted by ballvalve View Post
    If its been full of water for along time and your T&P valve is not leaking, I would cut it off and throw it away forever.
    Let's not start this controversy again...IF you need an expansion tank by code for your specific conditions, install a new one. Those conditions are: a closed system (created either by a PRV or a check valve) or your local code requires one regardless. If you don't have a closed system, unless your local code requires one anyway (some do), then and only then, should you consider eliminating it. IF the system needs one by code or specific conditions, not having a working one puts constant stresses on your water supply system, decreasing the life of things. It is cheap insurance.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    In the Trades Gary Swart's Avatar
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    I concur complete with jadnashua. I learned about thermal expansion tanks after I installed a PRV. Suddenly, my T/P valve was discharging water every time the water heater kicked on. I replaced the T/P (twice) and still have the problem. When I came to the forum with the problem and was advised to get a thermal expansion tank. I got one, installed it, and end of problem. Last time I checked, they cost about $50. If you can sweat a joint, they are simple to install. Just be certain it is well supported.

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    DIY Junior Member gabby's Avatar
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    Hey Thanks, I appreciate it very much. Sounds simple, just not want to mess anything up.

  8. #8
    DIY Junior Member gabby's Avatar
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    Actually I picked one up at HD for $60.00 an got it home but it was larger than the one on the tank so I took it back today an got the right size for $38.95. I have a 80gal water heater so I did not think this was high at all. I plan on installing it tomorrow. Thank for all the help from both of you.

  9. #9
    Retired Defense Industry Engineer jadnashua's Avatar
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    The expansion tank should be sized by the WH and the volume of the lines modified by the temperature differential from the inlet to the outlet. It may be that the old one was too small. This will cause it to fail earlier since it would require the bladder to stretch further with each cycle. Watts has a sizing calculator on their website...you may want to check that out even if you use a different brand.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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