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overpressure

ryan67ryan67 Posts: 2Member
evening guys,

i have an older 1988? HBSmith gas fired furnace, 2 heating zones.  i have issues with my safety blowing occasionally.  i just changed the expansion tank and 30# safety valve and old B&G circulating pump and it just burped again 2 days after the change.  i probably would have never known except the **** safety never resealed and i now i have a soggy basement.  any advice on what else could make me overpressure? i was going to block in the feed regulator and run it as a true closed loop but am unsure if this is a good idea.  not sure if this helps but after drainign and filling the system a few times i cannot keep clear water in the system, always brown

Comments

  • Mike Kusiak_2Mike Kusiak_2 Posts: 604Member
    edited November 2010
    Static pressure?

    What is the static system pressure when the system is cold?  Does the static pressure rise over time? I would try shutting the valve to the water feed and see if the system continues to overepressure. If this stops the problem then the pressure reducing valve is bad and should be replaced.



    I can think of it being one of two things. First, as mentioned above, if the pressure reducing feed regulator is leaking, the system pressure will continue to rise until the relief valve will blow off the excess pressure. Second, if the capacity of the expansion tank is too small, it will not be able to accept the volume of water necessary to keep the pressure under the relief valve setting when the system is hot.



    Why are you continuing to drain and refill the system?  In a closed system you do not want to be constantly adding new water because it contains dissolved oxygen and will cause corrosion. The rust you are seeing may be as a result of the multiple refills with fresh water.
  • Tim McElwainTim McElwain Posts: 4,281Member
    In addition to what

    Mike gave you do you have a tankless domestic water system (get hot water from the boiler) if so the coil could also be leaking and causing overpressure. Shut off the cold water feed to the coil and leave it and see if prressure increase stops, if so the coil is leaking.
  • icesailoricesailor Posts: 7,265Member
    Overpressure:

    If it is a HB Smith gas boiler, it may not have a tankless. If it doesn't, and is a cold start, I would suggest that the #30 Extrol tank is too small. It should be a #60. A cold start has far more hydronic expansion that a warm start. I believe that the extrol charts show a boiler like yours that is cold start, needs a larger extrol.

    I change a lot of cold starts to #60's.

    I (also) always change the pressure relief valve if they have blown off a couple of times. If the high limit is over 180 degrees, it may make water over 200 and water will "push" under the seat. It will boil off leacing a calcious product behind and start weeping. Also, the precharge of the tank must be set correctly. At or below the set pressure of the PRV.
  • ProfProf Posts: 7Member
    Cushion tank

    Like Icesailor mentions, check the preset pressure on your cushion tank.

    I notice that some wholesalers are selling DHW expansion tanks for boiler expansion tanks, (white = DHW / Gray = boiler) with one of the main differences (besides color) being that the DHW cushion tanks are preset to 40 psig. Instant problem for your boiler. The expansion won't be cushioned, instead the relief valve will open...
  • icesailoricesailor Posts: 7,265Member
    Cushion tanks:

    Prof,

    The different colored tanks are for homeowners who don't know the difference.

    But, I always wondered why the Extrol tank I bought for a hot water expansion problem was white and all the other extrols for heating were grey. Now I know.
  • Jean-David BeyerJean-David Beyer Posts: 2,642Member
    Expansion tank color.

    "Extrol tank I bought for a hot water expansion problem was white and all the other extrols for heating were grey."



    My expansion tank, from B&G, is red.  HFT-30  Precharge pressure 12 psi.



    I assume different manufacturers use different colors.

  • ProfProf Posts: 7Member
    cushion tanks

    Icesailor, the white tanks (Amtrol) are specifically designed for DHW, and besides the preset pressure of 40psi, they are polypropylene lined for corrosion resistance. The gray tanks (Amtrol) are not lined and are preset at 12psi.

    There is also a temperature and pressure rating difference.

    I don't know who makes the red cushion tanks.

    RYAN67 -- It sounds like the cushion tank is set properly, so then the culprit could very well be the PRV.

    Starting to sound like a professional needs to give your system a "good dose of looking on".
  • ProfProf Posts: 7Member
    RYAN67 overpressure

    RYAN67 -- Oops, I misread, you haven't replied to what your cushion tank was set at...

    I stick by my post about having a professional take a look...
  • icesailoricesailor Posts: 7,265Member
    Overpressure:

    Prof,

    The grey tanks have a liner also. They just have a max precharge of 30# and come set at 12#.

    When the tanks fail, you can often blow the water back into the system with a air compressor. If nothing happens, it unscrews easily. Right up until the last thread. Then, it will drop like a stone and it weighs more. Anything below it will be crushed. Like your foot. I usually tie a 5 gallon bucket to the piping and let it drop into the bucket. The blue ones for wells come with a 30# precharge which you set to the pump range pressure. Those, I drive a screw driver through and let the water flow out if I can't blow it.
  • ProfProf Posts: 7Member
    Amtrol tanks

    the Amtrol tanks (both grey and white) have bladders but only the white ones built for DHW have a polypropylene anti-corrosion liner. check out this link http://www.amtrol.com/pdf/MC4090%2007_10TXTBrochure.pdf  for DHW and this link http://www.amtrol.com/pdf/MC2680EXTROLBrochurelow.pdf for standard hydronic cushion tanks.
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