Boiler, Leaking pressure relief valve

Discussion in 'Boiler Forum' started by BobD777, Mar 20, 2020.

  1. BobD777

    BobD777 Member

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    Thanks in advance for your help on this!

    I've had a leak in a pressure relief valve coming off the boiler that is now being used only for DHW. I changed the relief valve, but it still leaks. So I'm now thinking about looking at replacing the system's pressure reducing valve (taco 329-3), since that could be adding water to the system when it's not needed. Make sense?

    EDITED: Then, I was told that the expansion tank might not be large enough for the size of the system. It's a #30 Extrol Expansion Tank (4.4 Gallon Volume) was just changed last year and sounds fine when I tap and check pressure.

    2 Questions:

    1. Am I correct in trying to change the pressure reducing valve next?

    2. Is the pressure the same on both sides of the pressure reducing valve? I know it only kicks in when the pressure goes below a certain point, but does it allow full system pressure through? I would think it does, but just making sure since that would determine if the pressure in my expansion tank is correct.

    I've done all kinds of construction for year, but am just now learning some of the finer points of plumbing systems.

    Thanks again!

    IMG_20200320_123610.jpg
     
    Last edited: Mar 20, 2020
  2. fitter30

    fitter30 Well-Known Member

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    Looks like a heating boiler not domestic hot water. Boiler should have a gauge on it. With pumps off water pressure should be 10-12 lbs on most houses. Expansion tank air pressure should be at water pressure and no water coming out of schrader valve. Is there another pump other than zone pumps? Does the water pressure vary with water temp? Relief valve 30 lbs?
     
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    If you have an autofill valve, that can leak, slowly (most of the time) raising the pressure. Another reason water pressure may rise is if there's a leak between the heating coil in the indirect and the potable water in the tank. Last, if the ET is either defective or improperly precharged. You can't check that unless you turn the boiler off, then relieve the system pressure, otherwise, the precharge value will just equal the system pressure.

    If the reduction valve is defective, obviously, that could be the source of your problem. Sometimes, it's some crud caught on the seal, and opening it fully can flush it out. But, they're pretty reliable, and thus, the more common reason for them to open is if your pressure is rising too far (most of the time, it's a 30psi device unless you have a quite tall building). FWIW, my boiler won't close the interlock unless the system pressure is at least 12psi, and they recommend about 14 for most normal situations.
     
  5. BobD777

    BobD777 Member

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    Interesting. I've opened the autofill valve to flush out the device, as you suggested. I'll need to wait and see if that made any difference, since the leak is intermittent. Do you know if the pressure is the same on both sides of the pressure reducing valve?

    Regarding the hot water heater, I'm about to change the tank anyway, so I don't have to worry about that.

    And yes, I think the pressure relief valve is 30psi. I'll check the expansion tank as you suggested.

    Thanks so much for the feedback.
     
  6. BobD777

    BobD777 Member

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    The pressure gauge on the boiler shows 20psi. And the relief valve is for 30lbs. There's no water coming out of the valve when tested. Should the expansion tank be pumped to 20psi, or to the house pressure of 65psi? If it's the 20, that would explain the leak.

    I haven't seen the water pressure vary with water temp, but I could be I haven't noticed.

    The boiler used to supply all those heating zones in the picture. But now that's not being used, since I'm on geothermal. The only circulator pump that is being used is for the domestic hot water. That's the green one at the end. Other than that, there are no other operating pumps on that system.

    Thanks for your time!
     
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Assuming you're talking the autofill valve, it's whatever your supply pressure is on one side, and whatever it is adjusted for on the outlet. IF it's leaking, the outlet pressure will typically rise, potentially up until the safety relief valve opens.

    The pressure relief safety valve should be open to the atmosphere on one side, and hooked into the boiler on the other.

    If the system is adding water frequently, that is not good for the system health...potable water will have some dissolved oxygen in it, and that, over time, will corrode any ferrous materials as they rust. IF properly sealed, once all of the oxygen is used up, it's pretty stable. A steady stream of fresh water will shorten the life of the system components.

    The ET precharge should be your normal, system pressure (seems yours is sitting at 20, so the tank should be pumped to that). 20psi is a bit high for a typical home...12-15 is more normal.
     
  8. BobD777

    BobD777 Member

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    Yes, I was talking about the autofill valve. And if I'm right, you just put your finger on the problem. My ET is set for the house pressure! So I'm going to drop the tank to 20 right now. I'm feeling very positive about this...

    Had no idea about the dissolved oxygen. The more I learn, the more I see how much I don't know.

    Thanks again and I'll post the good news soon :)
     
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Note, you may have two ETs in your home:
    - one for the potable water and that should be set to your normal incoming water pressure
    - one for your boiler, and that should be set to the boiler's normal pressure.

    Setting the potable water's ET to 20 could damage it when you turn the water back on and start the water heater's T&P safety valve to open if you have a closed system (your boiler's system is closed, that's why it needs an ET...many utilities also make your supply a closed system as well, which is why you may have two).

    There cannot be pressure on the open side of the ET...to get that, you need to relieve pressure in the system and leave a valve open to then adjust the precharge.
     
  10. BobD777

    BobD777 Member

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    The cold water supply line does split into two branches. There's an ET on each branch. One branch that is for the boiler goes to that autofill valve we've been talking about (near the expansion tank in the picture above) which goes to the manifold where all the circulating pumps are. The ET on that line is after the autofill valve. This is the one I turned down to 20psi.

    The second branch, as you said, for potable water, goes to the cold water inlet at the bottom of the hot water tank. This one is at the whole house's psi.

    After lowering the pressure on that first tank, the pressure relief valve is still leaking. I'm surprised. What are the possible villains now? Do I change the autofill valve?

    Not sure what you mean by this: "There cannot be pressure on the open side of the ET...to get that, you need to relieve pressure in the system and leave a valve open to then adjust the precharge."
     
    Last edited: Mar 20, 2020
  11. fitter30

    fitter30 Well-Known Member

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    Is the pressure in the boiler still at 20 lbs and relief leaking or did the pressure creep up. If it did lower pressure back down to 20 lbs and valve water regulator off . Keep a eye on the boiler pressure for 24 hours and if water pressure raises coil in water heater is compromise.
     
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  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    To precharge an expansion tank, you must relieve all pressure from the working side. Generally, to do that, you have to shut the system down, open a valve to relieve all pressure, precharge the ET, then re-pressurize the boiler system. Otherwise, when measuring the pressure on the ET, all you're doing is measuring the water pressure, not the precharge...the water and air pressure will equalize each other. IF the tank's precharge is higher than the boiler's, then, you could read that higher pressure, but it's unreliable to leave the boiler's pressure up when trying to adjust the precharge...water isn't compressible.

    The relief valve is a safety device that should not open except in a fault condition. IF it does, on a regular basis, it may need to be replaced. FIrst, though, you need to adjust the precharge properly to see if things are resolved.
     
  13. BobD777

    BobD777 Member

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    OK. Finally got some time to put into this... I did what you said in terms of adjusting the precharge of the ET. First off, before I did anything, the boiler pressure when I first checked it was 15psi. So I turned off the system, opened a valve and brought the boiler pressure to zero. Then I checked the ET pressure and it was 25psi. (Not the 20psi that I had set it at without shutting the system.) So I reduced the ET pressure to 15psi. Then I repressurized the system.

    As the system filled, the boiler kicked in, and the boiler pressure kept rising over to over 30psi. Then the pressure relief valve opened and it went down to around 20psi. I then tried opening a valve to let the pressure drop low enough for the pressure reducing valve to kick in. Each time I did that, the boiler pressure went to between 17 and 20psi.

    Been watching it and over the last hour or two and the pressure seems to be hovering in a range from 17-22psi. And, the pressure relief valve is still leaking. It was dropping 20 drops or so every 10 seconds. So I turned it on fully to clear out anything that might be stopping it from closing. Since doing that in the last hour, the rate varies from one drop a second to one every 30 seconds.

    When the pressure went up to 30psi, I thought that the pressure reducing valve wasn't working--staying open too long. But then, since the system is still leaking even when the system pressure seems steady, it seems like the pressure release valve. Can it be a combination of the two, even though I changed the pressure relief valve just a couple of months ago?

    Phew!
     
    Last edited: Mar 23, 2020
  14. BobD777

    BobD777 Member

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    If it helps, I just wrote another post, above, explaining what's happening now, after turning off the system and more. Does that tell you anything? I'm more confused than ever o_O

    As per your recommendation, I'll start keeping an eye on the pressure for the next 24 hours. So far, this morning it was 15 and now it's been hovering between 17 and 22psi.

    PS: That's one good looking dog. Your family?
     
  15. fitter30

    fitter30 Well-Known Member

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    Yes he's one of two collies. He's a scotch or some people call them farm collies. My other is a rough coat looks like lassie. Give the boiler another couple of days see where the pressure goes. Regulator is probably bad because wasn't pressure going up every day and causing dripping relief valve.
     
  16. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    The safety valves aren't really designed for constant usage, so it could be bad. The pressure will go up (slightly) when the system is running, but if the ET is sized and pre-charged properly, not much. WHen the ET is overpressurized, it limits the amount of expansion volume available, and that makes the pressure rise more likely to be a much steeper slope.

    Have you run the calculation on what size ET you should have? Most of the manufacturers have a calculator on their website. But, you need to get a fairly accurate assessment of the amount of water in your boiler system for it to be valid. If it's too small, your pressure will go up faster. Other than the physical size and the increased cost, a larger one will have a lower pressure rise than a smaller one. Overpressurizing it makes it function like a smaller ET.
     
  17. BobD777

    BobD777 Member

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    I have done the calculation and what I have is plenty sufficient.

    I'm guessing that the valve is bad, since it's incessantly dripping. I'm going to change it again tomorrow. Makes sense that the ET might have been the initial cause, since it was WAY too pressurized.

    Once again, I'm feeling very positive about this working... again :)

    Thanks and I'll report back with the good news soon--
     
  18. BobD777

    BobD777 Member

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    He's a beauty. I haven't had a dog for a while, but have had a bunch of amazing cats. Our current boy is very much like a dog in many ways.

    Since the pressure relief valve is still dripping, I'm going to change it. I've got an extra on hand. I will then watch the pressure and all for a couple of days. I had the ET pressure way too high... for perhaps the last year!
     
  19. BobD777

    BobD777 Member

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    Well Jim, I think we're done here. I've read elsewhere that the pressure relief valve ought not be used too often, considering this one was dripping incessantly, it was definitely messed up. I changed it and for the moment, all is looking great. Time will tell.

    Thanks for sharing your wisdom. It was very helpful!
     
  20. BobD777

    BobD777 Member

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    I just changed the pressure relief valve, and so far everything's looking good. Fingers crossed. It must have been the excess pressure in the ET for all this time that kept wrecking the pressure relief valves. Simple, in hindsight.

    Thanks for your help!
     
  21. Terry

    Terry Administrator Staff Member

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    That's the first thing to check, sorry. I always carry spare T&P's on the van.
    Typically if you don't touch them, they last as long as the water heater. In theory, you test them every so often. Doing so, it's a good idea to have a replacement on hand, because once you start check them, they can quit sealing.
     
    Last edited: Mar 24, 2020
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