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Temporary fix for pressure relief safety valve?

Stew_5 Member Posts: 23
 I don't want to mess too much with a working, unknown, ancient system and It's too cold, and is going to remain too cold, to shut my Weil-Mclaine boiler down for a pressure relief valve change.  The valve is leaking off about a quart of water a day. I don't like all that new water going into this old iron pipe and cast-iron radiator system. Can I just add the new replacement valve,in-line, after the existing leaky one? Or is it temperature dependent also?  It's a very old house we just purchased last fall. Lots of pipe in the roof/attic space from the old gravity system that would probably freeze up by the time I got the boiler cooled down enough to change the valve out. 


  • Jamie Hall
    Jamie Hall Member Posts: 22,918

    No, you can't.  That is to say, it's not safe to do so.  A pressure relief valve must -- no exceptions -- exhaust to the atmosphere; no valves between it and the pressure vessel it protects, and no valves between it and the atmosphere.

    That said, a weeping pressure relief valve is telling you something: something is amiss in the system.  It should never reach the valve setting; in fact, ideally it should never reach close to the valve setting.

    I'm assuming that this is a hot water system?  Is it still gravity, or does it now have circulating pumps?  Either way, somewhere on the system there is -- or was -- provision for expansion.  It may be an expansion tank in the basement -- either one of the newer ones with a bladder, or one of the older ones which depends on air over water.  If you can find it, you need to be sure that there is air in it, at the proper pressure.  If there isn't, you need to fix it.  We can help you with both of those things, but we need to know what we are dealing with to help!

    On the other hand, if it is a really old system, there may be an open or vented expansion tank in the attic.  If it's really cold up there, could that have frozen?  I can envision a scenario where the attic floor got insulated... and the expansion tank froze as a result.  See if there is one up there, if you can't find one in the basement.

    A little more exploration on your part, I'm afraid... but let us know what you find.

    And do this fairly quickly.  There is no point in replacing your pressure relief valve before you find out why it is releasing -- but equally, there is no time to waste before you find out why it is releasing, and fix that!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Ironman
    Ironman Member Posts: 7,350
    Are You Sure...

    That the valve is bad? What's the pressure on the boiler when it's hot? Is your expansion tank water logged?

    If the system is still gravity flow, the tank may be in the attic. Or you may have no tank at all; in this case, the top of your radiators has to maintain an air cushion for expansion. If you bleed all the air out of them, then there's no place for the heated water to expand and the relief is doing its job. If you can't find a tank, and the rads are piped across the bottom (in and out), then this is what you have.

    Your fill valve may also be over-filling the system. To check this, simply close the shut off valve in the feed line and see if the pressure levels off or keeps climbing. This may take several hours to confirm.

    If you do have to change the relief, I would not put another in series with it. If the old one sticks shut, then the new would be rendered inoperative and you would have a potential bomb on your hands. I've seen a boiler blow up and go through two concrete walls from this happening. The kinetic energy of an exploding boiler can be devastating.

    A better approach would be to simply close the fill line, drain the system until you have zero pressure, have the new relief doped and in hand. Then unscrew the old one, place your thumb over the hole to stop water from gushing out and quickly screw the new one on. Then refill the system and bleed air as necessary taking heed to what I mentioned above, if you have that setup.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • icesailor
    icesailor Member Posts: 7,265
    Air in Radiators:


    In a hydronic system with radiators, there should NEVER be any air in the radiators. Air in the radiators contribute to corrosion. But worse, if the water level in the radiator sections don't go onto the top nipples, you will not get proper circulation through the sections. When the water goes in one side, it flows up the first section and up to the top. Pushing cold water out the bottom on the other end. The hot water ends up on the other side and there is a diagonal line of hot radiator from top opposite side to the bottom of the hot water side.  If you feed a radiator on only one side, and you have the feed into the bottom and the return on the top, it may just short cycle and only the end section gets hot. If the hot is in the top, the cold runs out the bottom and the radiator gets hot. Unless the radiator is too long in which case, the whole radiator doesn't get hot. Unless you put a pipe in the top to make the water go to the other side of the radiator. I've done that. More than once.
  • Ironman
    Ironman Member Posts: 7,350
    I Know...

    What you're saying, Ice. But old timers did this sometimes. We just recently converted one of these to forced flow with a mod/con and it definitely got an expansion tank then.

    The trick to filling this old type of system is to get the water level to about an inch from the top in each rad. That way there is flow through the rad, but the air cushion of all the rads combined is sufficient for the expansion of the entire system.

    As far as the corrosion issue goes, my thinking is like yours. I don't care for the design, but the one we just converted had been that way for 100 years and still had all of the original rads. The Dead Men must have understood something that we don't see.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Ice, what Bob said is true...

    I have seen a couple of older systems that had NO expansion tank ANYWHERE.

    The systems were gravity, with the radiators bottom tapped for in and out.

    Following your lead and the need to bleed, I incorrectly bled all the air out of the radiators, only to be called back the next day for water on the basement floor. Being a young dummy, I replaced the relief valve, lowered the operating pressure, and ended up back there agin the next day for the same reason, water on the floor.

    This time, I replaced the pressure reducing valve. Thought I had it fixed.... only to be called back AGAIN the next day, for water on the floor.

    A complete and thorough search determined that there was NO expansion tank ANYWHERE in the system.... I added one, and later that night did some serious reading of Dan's books, and discovered the expansion tank-less systems that the dead men left us with.

    Those tricky old dead men DID know what they were doing... It's us YOUNG punks that can't figure it out.

    You (and anyone reading this) learned something new today :-) Consider it a good day.

    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.
  • Stew_5
    Stew_5 Member Posts: 23
    Additional background info

    Sorry, I should have given more info. It's hydronic.  There used to be an old style expansion tank. I'm guessing there was one originally in the attic space with the original boiler, then another one in the basement just over the boiler (old straps are there). It now has a pretty new boiler w a bladder expansion tank. System pressure is 20-25 lbs, checked expansion tank, not water logged.

    The plumbing and installation is bad enough to be worth a picture or two.

    It was originally a gravity system. Piping still goes all the way to the attic space (not for long, I'm planning). There's a anti-gravity unit that keeps the hot water from circulating when the circ. pump is not running; otherwise it will gravity flow backwards and return to the TOP (!!!) of the boiler. Yeah, it's worth some pictures. Whoever put it in obviously had some expensive equipment, but were lacking in some other departments.

    The fuel bill must have been through the uninsulated roof. When we moved in, the gravity check valve was positioned for convection circulation, so the boiler was on pretty much all the time, circulating all the water through every radiator (one zone) and all the old gravity piping in the attic, then back down to the top of the boiler.  So the return side was very hot and the top was quite a bit cooler.  Ouch. Ouch ouch ouch.

    Back to my relief valve. It leaks little burps even when the boiler is off. I guess a tandem pressure relief is a Bad Idea, so I'm thinking of covering the aquastat with some tarp and putting on insulated rubber gloves, turning off the make up valve and making a quick change with the new valve open so I'm not fighting the pressure.
  • Ironman
    Ironman Member Posts: 7,350
    Stew, I'm Still Not Sure...

    That your relief is bad. The bladder (air) side of your expansion tank may not be properly charged. Or the tank may be too small.

    With zero water pressure, the air side of the tank should be charged to 12psi for a two story house, 18psi for a three story. The fill valve should be set to the same.

    What is the model number of your expansion tank and how many btu's is your boiler? Is it gas or oil? Does it have a domestic coil in it or an indirect?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Stew_5
    Stew_5 Member Posts: 23
    More info

    Thanks Bob,

    It's an oil fired, Weil McLaine, 126000 btu, model P-WTGO-4. Has a domestic coil (I'm interested where that question may lead). The expansion tank is an Amtrol Extrol model 30.

    If the relief valve, which is  30 psi, is leaking water at 12-15 lbs, then how can it not be a bad valve? I agree that the leaky valve may be just a symptom of another problem and don't want to replace it till I have an idea why it's failing.

    I was incorrect on operating pressure; it's more like 12 to 15 lbs according to the gage on the boiler. The expansion tank is measuring 20- plus lbs when boiler is off, although I only measured it with a cheapie tire gauge.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,700
    edited March 2011
    Timeless Practice

    I would think the practice was used to same money , maybe the attic tank rotted out , the copper tanks could have gone to the war effect or to put food on the table .. Not the greatest system for reasons Ice and Mark mentioned ... It would be rare to come across one today.. I could only remember one... Same story as Mark . I was there all night and even returned the next day . Brings to mind of an open system after installing a pressure reducing valve, try adjusting it.... Four flights up, four flights down, four flights up .............................four flights down...... the test is, how long before one gives up LOL

    Oh the relief valve which is a Pressure Safety valve change it out..It's there so your system does not blow up.. Call in a good plumber for this one . He may not have to drain down the system and you don't want to break it off ..
    I have enough experience to know , that I dont know it all
  • Ironman
    Ironman Member Posts: 7,350
    Gauge Bad?


    I wouldn't trust your boiler gauge. Also, you can't get an accurate reading from the air side. In fact, the water pressure may actually be higher. If memory serves me correctly, 1 psi air will hold 2.31psi water (may have to check this).

    Your expansion tank is under-sized. According to Extrol's sizing tables, you should have a minimum of a 60. I never put anything smaller than this on a gravity system and quite often go larger due to the volume of water in the larger pipes.

    Regarding your domestic coil: If it leaks, it will over-pressurize the boiler due to the higher pressure in it from the potable side. You would have to isolate it for a while to test.

    I'm not saying that you won't have to change your relief valve. I'm just going on the proper assumption that when a safety devices operates we assume it's doing its job and find the cause before assuming it's the culprit. But you should increase the size of your Extrol to at least a 60 or even a 90. Over-sizing on this is not harmful, under-sizing is.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • icesailor
    icesailor Member Posts: 7,265
    Expansion/Extrol Tanks:

    I seriously doubt that a #30 Extrol tank is big enough for your system. I would either replace it with a #60 or leave the #30 and add a #60. That expanding water pressure has to go somewhere. A WTGO has a tankless coil. That may have an issue too.
  • Stew_5
    Stew_5 Member Posts: 23
    Pictures. Please comment

    Looks like the immediate problem is a corroded, weepy safety valve. I checked pressure w/ a new gauge and it pretty much matches the boiler gauge. Also realized that changing the safety valve should be pretty easy because at least somebody put in valves on the return and supply side.

    But how about this installation?  When it warms up this June, I'm planning to replumb at least all the radiator returns w/ pex and eliminate all 2nd floor piping (there's only one radiator left upstairs and that whole floor is not going to be anything but an attic for awhile). So I'll replumb most of what's pictured here, including the fuel line, which currently doesn't let you swing the burner out.  I figure on adding a  supply manifold  for future pex supply lines to the radiators and a few extra for possible attic renovation.

    Any suggestions, observations would be appreciated!
  • Ironman
    Ironman Member Posts: 7,350
    A Few More Pics...

    Of your near boiler piping would be helpful. I'm not getting the piping layout clear yet.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
This discussion has been closed.