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Expansion tank kaput.....

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Roland_18
Roland_18 Member Posts: 147
in THE MAIN WALL
After 5 years, my THERM-X-TROL ST-5 gave up. I gave it a tap with a screwdriver on the top and bottom and it gives a dull thud. Curiously, this tank is on the hot side of my Super Stor 35 indirect. The tank on the boiler gives a nice metallic ring when tapped on the underside.

Do I really need an expansion tank on the indirect? The I/O suggests a tank on the COLD side. Maybe I'm not paying attension to the pictures others have posted,but, I don't recall seeing expansion tanks on hot water heaters, indirect or otherwise.

Thanks, Roland..........

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  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    edited January 2012
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    should be

    on the cold side.  Most manufacturers recommend it.  Are you only basing the failure on the sound it makes when you tap on it (yikes)? Or is something else going on. "Do you really need it".....only if you want to try to make a warranty claim when it fails

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  • lchmb
    lchmb Member Posts: 2,997
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    it's

    a good rule of thumb to have one (a cheap insurance for the tank)..I would however switch it to the cold side of the tank and make sure when they install it they set it to your incoming water pressure per specs...
  • Roland_18
    Roland_18 Member Posts: 147
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    Expansion tank kaput.....

    I have a habit of checking the boiler and associated equipment on a daily basis. Call me crazy but I have this fear of a minor leak turning into something more exciting. I tap on the expansion tanks as a matter of course and always (until this morning) have heard a metallic 'ring' when hitting the air end. I am assuming the DHW tank is waterlogged due to the dull thud when hit.

    I can't say I'm surprised that it failed as it was not probably not adequately pressurized when installed. I think I'll remove the tank this weekend as it probably has about 30 pounds of water in it and I don't trust the piping to support this kind of weight. Ahh the pleasures of home ownership!
  • lchmb
    lchmb Member Posts: 2,997
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    one thing

    dont drop it on your foot...Trust me, it hurts...
  • redhawk
    redhawk Member Posts: 9
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    Expansion tank kaput...

    I had exactly the same tank fail in my system, and thought I would alert you to this rather scary result...

    After replacing it, I took the old tank and drained it.  I could not believe the black gooey liquid that came out of it...!  Don't know how long that stuff might have been seeping into our drinking water.  I can only conclude it was the remains of the decomposed rubber bladdder.  ughhh....!!

    -

    To prevent the same thing in the future, I installed a pressure relief valve that would crack at 75 psi and release water thru an unused DHW relief pipe out the back of my house.  My normal pressure is 55 psi and DHW tank relief valve is 150 psi, so this is about halfway between.  The idea is if I see water coming out of that pipe, I have a failed expansion tank...!

    The first x-tank failed after 10 years.  Interesting that yours barely made the 5-year warranty.  Probably failed early because of the HOT water in it....

    I'm no plumber, but it seems to me the x-tank should go on the COLD side if only to prolong the life of the tank.  Hot water is gonna eat up the rubber much faster than cold.  Should make no difference to it's function unless you have some arrangement of valving that shuts off flow between hot and cold side.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    WHEN potable tanks are necessary....

    On city water systems, if there is a check valve between the heater and the city water main, you MUST have a potable water expansion tank. If no check valve (watch the water meter, some have internal checks) then no expansion compensator is necessary.



    On a domestic well system, again, if there is no check valve between the DHW tank and the wells pressure tank, then no expansion tank is necessary.



    As for whether its on the inlet or outlet, functionally, it makes no difference. Life expectancy wise, it MIGHT have some bearing (doubtful, based on closed loop heating systems experience and location) but to be safe, follow the manufacturers recommendations.



    Honestly, it sounds as though there may be a LOT of this particular brand of failed tank out there...



    In all of the above examples, the expanding fluid will either find relief through the connection to the city main, or the potable water pressure tank.



    ME

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  • Ron Jr._3
    Ron Jr._3 Member Posts: 603
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    Only problem

    installing the tank on the hot side is sometimes you might get a spurt of hot water from the cold of a faucet .



     If no one opens a tap while the indirect is replenishing , sometimes the pressure goes higher than street pressure . Until the pressure comes back down to normal ( and those charged up tanks can push alot of water out ) you might get some hot water in your cup to brush your teeth in the am !
  • Roland_18
    Roland_18 Member Posts: 147
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    Sooooo....

    Do I actually need an expansion tank on the cold side if no back flow prevention exists?

    The I/O shows a piping diagram with both, but, it doesn't seem to 'require' them.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited January 2012
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    One way to find out...

    Put a maximum pressure recording gage (Slow Hand) on the drain cock, and let it run for 24 hours. If you see a significant increase in maximum pressure, then yes, you need an expansion tank. If the pressure remains relatively stable, then no, tank not necessary.



    All tanks will "balloon" if exposed to excess pressure.



    Heres a link to a picture of the recording gauge.



    http://www.google.com/imgres?q=watts+recording+maximum+pressure+gage&hl=en&client=safari&sa=X&rls=en&biw=1222&bih=615&tbm=isch&prmd=imvnsb&tbnid=KTZmzaLTvzBTGM:&imgrefurl=http://www.houserepairtalk.com/f33/ceramic-disc-cartridge-failure-6266/&docid=6qBvZHX1jhV_JM&imgurl=http://www.watts.com/prod_images/hi-res/276H300.jpg&w=600&h=600&ei=dhgKT9qwHLDTiAL98sjJDg&zoom=1&iact=hc&vpx=460&vpy=271&dur=146&hovh=225&hovw=225&tx=132&ty=136&sig=105195322594521953864&page=1&tbnh=140&tbnw=134&start=0&ndsp=22&ved=1t:429,r:10,s:0



    ME



    EDIT: I forgot to mention that during the test you do NOT want to use any appliances that consume hot water and have an ON/OFF solenoid connected (clothes and dish washers) or you are guaranteed to see a spike in pressure, but it is kinetic energy and not expansion energy that would cause the spike.



    Just do normal showering, face and hand washing washing etc.... Otherwise you will get a false positive.



    ME

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  • Roland_18
    Roland_18 Member Posts: 147
    edited January 2012
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    Lazy hand test.......

    Thanks for all the helpful info. I did attach a non-recording water pressure gauge to the cold water supply and got a static reading of 50psi. I'm  going to scare up the the lazy hand gauge today.



    Thanks again, Roland



    p.s. What would be an appropriate replacement for the failed Therm-X tank? Also, it was the ST-12 not the ST-5.
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