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Testing relief valves?

Jean-David Beyer
Jean-David Beyer Member Posts: 2,666
Plumbing codes seem to require that the drain pipe from a pressure relief valve, or a pressure & temperature relief valve should be directed towards a drain or a floor, and terminate not more than six inches from the floor. The pipe is not allowed to be threaded or any valves, etc., inserted in there.

In the past, my boiler had no pressure relief valve, and my hot water had one that terminated a foot or so from the floor. Testing the valve was easy: I put a metal bucket under the drain pipe, pulled the lever, and when it appeared clean, I released the lever.

Now I have a new boiler and DHW heater, the drain lines comply with the code.  Since I do not want to slop the water onto the floor except in an emergency, what is the right way to catch the water? I cannot put a hose on there, and the bucket will not fit.


  • hot_rod
    hot_rod Member Posts: 21,868
    build some short ones

    most are threaded in loosly, remover the long ones, install the shorties for testing and replace the long ones after the test,.

    I used compression adapters on some of my relief valve discharge tubes. This allow easy valve replacement, without cutting or soldering (for top mount T&P's)

    Some times when you pop a relief valve they don't seal back off completely. While it is a good idea, and code required in some places I like to have a spare on the truck when I pop them, just in case.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    build some short ones

    That is a great idea. But I am neither a licensed plumber nor the contractor who installed the system. It is going to take them some work. Right now there is a T where the supply exits the boiler on the top. In the side of the T is a street elbow that the pressure relief valve is screwed into. The boiler manufacturer supplied the T, the street elbow, and the relief valve and said to hook it up that way. Unfortunately, they then soldered  an NPT fitting onto a copper elbow and from that elbow that is also soldered, the drain goes down to the floor. Behind everything. There are now some supply pipes blocking that.

    It looks to me as though they will have to cut off the existing drain pipe. Then they can remove the NPT fitting and the elbow. Then they can tighten the pressure relief valve 1/4 turn (if they can) and put in an NPT straight piece of pipe, an NPT elbow, and then a long pipe with an NPT thread on one end. And supply me with another pipe like that, but about a foot shorter.

    I see how it happened that they did it the way they did. But that is no excuse, I think.

    Because now, unless it weeps profusely, I will never know that is happening. And they will have to cut pipe to replace the valve. And I will not like to test it the way it is. Fortunately, it is only 3 months old, so it is probably OK.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,537

    Just change them if you feel that strongly about it,the leak rate on boiler reliefs is 75% or better,T&P valves are aq lot lower but still many will leak
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Just change them when?

    The way my boiler's relief valve is plumbed, I cannot see the water coming out of the drain pipe unless there is so much that it make a puddle under my boiler enough so that the water comes out the front. So the "just change them" model does not seem to work. First of all, I have to unsolder the drain pipe from the elbow coming out of the valve, or cut the pipe off. Only then could I change the valve. Should I do that once a year? Once a month? Once a week?

    Having the plumbing changed so I could test the valve, and also change it, seems to be less work than leaving things as they are and changing the valve instead of testing it.

    I agree that it would be smart to have a replacement valve on hand for the case that it did not close properly after a test.
  • Glen
    Glen Member Posts: 855

    I must ask why folks have an overwhelming urge to pop the safety from time to time. I know this will cause some wrath but here goes: at best smaller safeties or relief or T&P valves are fickle. An alarming percentage will leak/weep/drip new out of the box. So why test fate? Let them do their job when it is necessary - sure a visual from time to time is needed. But it is my experience that fingers should be left in the pocket - let those safeties rest gently.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Homeowner's manual requires it, among other things.

    The homeowner;s manual for my new boiler and my new indirectly fired hot water heater both require that I test these valves monthly. By checking, I infer they mean look at the drain pipe for discharge. The manual further requires that I operate these valves every six months.

    From what I read about these valves, mineral deposits can form around the valve seats, especially if they weep slightly, and basically freeze them up so they cannot operate when conditions occur where you would want them to open. So operating them will reveal if they are able to operate when necessary.

    My guess is that people do not want to operate these valves because if a bit of grit gets into them and prevents them from seating properly, that they will be allowed to remain in this condition and that will hasten their becoming inoperative. Some say if you operate them regularly from new, this is less likely to happen.

    I know I tested my old hot water heater (electric, but that probably does not matter) once a year, and sometimes it would not shut off completely. But I was lucky and operating it once or twice more cleared the crud out and it seated again as it should.

    Of course, it could happen that the valve did go bad, and by Murphy's law, this would be on New Year's Day and no one would be able to fix it, and the supply house would be out of stock on the valve I needed. Now I am not dumb enough to test one of these things on such a day, and I could be persuaded to buy a spare valve and keep it around for just such an eventuality.

    Since I am not a professional, I have to evaluate whether the boiler maker, the contractor, or the guy down the street knows best. I can probably rule out the guy down the street, but when the contractor and the boiler manufacturer disagree, what should I decide? I think I would rather risk replacing a valve unnecessarily once in a while, than have a bomb go off in my attached garage.
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