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relief valve

I have a 14 yr old 180,000 btu boiler used for radiant floor heating in a 3100 sq ft house. 5 zones. Heat exchanger blew out. Upon arrival found the flue was inproperly ran to roof, prv set @ 3psi, expansion tank and fill piped into discharge side of pump and no air vents in high points of piping. After rectifying all these problems, boiler starts and runs with a 17 degree delta thru boiler, psi on suction side of pump is 11 and 21 on discharge, shuts down off temp at 150 (setting) or satisfies on home stat. Only problem is upon next start up, the relief valve blows and causes knocking noise that wakes the dead every time, even though the psi in heat exchanger is below the 30lbs that the relief is set at. Anyone had any similar experiences? I'd appreciate any ideas. By the way, boiler ran for 14 years before blowing out heat exchanger with those problems mentioned before. ( save the prv setting which probably caused the exchanger to go out)

Comments

  • JStar
    JStar Member Posts: 2,752
    Water feed.

    Where is the water feed piped to in relation to the pump and expansion tank?
  • bockchoi26
    bockchoi26 Member Posts: 6
    WATER FEED

    I installed a tee on suction side of pump approx 24" from pump, in which I come off with length of pipe and tee again for my fill and continue to my expansion tank
  • JStar
    JStar Member Posts: 2,752
    edited March 2010
    Height.

    What's the height of the highest system pipe in the house? Also, how much pipe is between the supply pipe and expansion tank, and what size?
  • bockchoi26
    bockchoi26 Member Posts: 6
    hieght

    the highest pipe is about 3.5' (radiant floor heating) just to and from boiler, and about 3' between xpansion tank and supply. Supply and return piping is 1 1/4" and pipe to expansion tank is 3/4"
  • JStar
    JStar Member Posts: 2,752
    Pressure.

    Try adjusting your pressure back down to about 6 psi. If the pump is giving you a 10 delta P, you're coming pretty close to the relief pressure. It sounds like water is being fed in when the pump runs. Since the highest loop is less than 5 feet above the boiler, you won't need a lot of fill pressure.
  • rha
    rha Member Posts: 2
    rha

    If the prv is piped at the expansion tank (point of no pressure change)  and the suction side of the pump then either tank is no good or its too small. This is assuming prv is not leaking by.
  • rha
    rha Member Posts: 2
    rha

    If the prv is piped at the expansion tank (point of no pressure change)  and the suction side of the pump then either tank is no good or its too small. This is assuming prv is not leaking by.
  • jhill
    jhill Member Posts: 7
    relief valve

     In your post above you state the relief valve blows even though boiler pressure is below 30 psi. If this is true then its a bad relief valve plain and simple. Don't go on a witch hunt.
  • jhill
    jhill Member Posts: 7
    relief valve

     In your post above you state the relief valve blows even though boiler pressure is below 30 psi. If this is true then its a bad relief valve plain and simple. Don't go on a witch hunt.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Which hunt??

    I've seen more bad gauges than I have bad relief valves....



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • bockchoi26
    bockchoi26 Member Posts: 6
    witch hunt

    with boiler off I fast filled system and found relief blows at 24 psi. system pressure is 12 pump increases it to 22 psi. changed out relief and its been workin fine. thanx 4 the help, after all the work done, it comes down to a defective relief!!
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