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    slickjy's Avatar
    slickjy Posts: 6, Reputation: 1
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    #1

    Nov 25, 2009, 12:53 PM
    Hydronic system relief valve keeps popping
    I have an in-fllor basement hydronic heating system, using a standard, dedicated hot water heater. The system's worked great for the 8 years we've been in the house, which is 14 years old. Earlier this year, the hot water heater's pressure relief valve was leaking water through the overflow tube. When heating season came back aroundthis fall, I drained the water heater, replaced the valve & re-filled the heater. Unknowingly, I replaced a 30 psi presssure relief valve with a 150 psi temperature and pressure relief valve. Fearing that would create a problem, I replaced that with the proper 30psi pressure relief valve, exactly the same as the original that I had. I did that without draining the tank fully, and with hot water still in the tank. When I attempt to re-fill the tank, the pressure valve opens and freel gushes water. Any advice as to what I've done wrong, or what I have neglected to do at all? Could I have damaged some other part of the system when the 150 psi valve was in use?

    I don't know much about these things, so any hel will be greatly appreciated.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #2

    Nov 25, 2009, 01:19 PM
    Check your expansion tank. It is probably full of water which does not allow the water as it heats up any place to expand to. On newer systems it looks like this. Your were smart to change out the 150 PSI valve since that could have caused things to go BOOM. Most all residential systems are max 30 PSI.
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    slickjy's Avatar
    slickjy Posts: 6, Reputation: 1
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    #3

    Nov 26, 2009, 12:13 PM

    That is what my expansion tank looks like... Pardon a silly question... How do I "check" it?

    Thanks for helping!
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #4

    Nov 26, 2009, 03:27 PM
    Usually you can tap on the tank about 6 inches from the bottom and it should ring or sound hollow. That usually means it is not full of water. The tank has a bladder in it that separates the air from the water. The lower part of the tank comes from the factory with 12 PSI of air pressure in it which is good enough for a single story home.

    Thre is a shrader valve in the bottom of the tank that is used to add or remove pressure. If the ringing out of the tank does not tell the tail then a slight discharge of air from the bottom of the tank will. If ANY water comes out of the air valve when the center is pushed then the tank has a internal leak and must be replaced.

    NOTE do not let all the air out of the tank or you will have to recharge it to 12 PSI instead just leave a LITTLE air out since if water is present it will show right away and this way you will not have to recharge the tank if the tank is still good.
    tk03's Avatar
    tk03 Posts: 33, Reputation: 2
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    #5

    Nov 26, 2009, 06:39 PM

    There should be gauge to watch so the refill pressure does not go above 12 psi. To check the air charge in the tank you need to have "0" water pressure in the tank. If the charge is low you can use a bike pump to pump it up to 12psi.
    slickjy's Avatar
    slickjy Posts: 6, Reputation: 1
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    #6

    Nov 27, 2009, 09:09 AM

    Thanks, all. The tank rings hollow & the valve emits no water when I et out a LITTLE air. The hot water heater has ben empty & pilot has been off for a few days now, so I will refill the hot water heater today with fingers crossed that the pressure valve holds!
    slickjy's Avatar
    slickjy Posts: 6, Reputation: 1
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    #7

    Nov 27, 2009, 10:18 AM

    Nope - the pressure valve still pops open. I verified again, no water coming out from schraeder valve of expansion tank. So, if expansion tank is OK, the only other cause is that the new 30 psi pressure relief valve I installed is faulty... correct?
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #8

    Nov 27, 2009, 12:01 PM
    If no water from tank it should be OK. It is very rare that a new pressure relief valve would be defective when new as long as it is a 30 PSI model since the system is supposed to be operating at 12 PSI or lower since you have in floor heat in the basement only or does the hot water heat also do the first floor??

    Question? Is there a pressure gauge located in the hot water boiler line? Now we are not talking about the expansion tank now but the water line that feeds your in floor heat. It is possible the valve that controls the fill water pressure of the heat system is defective. If you need an explination of this part and what it does just ask but you seem to know your way around your heater. A simple answer is the fact that the cold water feed water pressure from your homes cold water line has to be kept at about 12 PSI also and if the automatic feed valve is defective or out of adjustment it will also cause the system to have too much pressure and it will pop the pressure safety valve. This is just about the last thing that can cause the problem you are having since you already tested the tank. The pic below is of a combo feed and relief but it will give you an idea of what to look for.
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    slickjy's Avatar
    slickjy Posts: 6, Reputation: 1
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    #9

    Nov 27, 2009, 01:00 PM

    Yes - there is an in-line pressure & temp gauge, on the feed line that goes to the floor tubing. It is in-line after the circulating pump. That gauge shows 12 psi and has never changed through this whole ordeal. The fill valve is a Bell & Gossett Reducing Valve with a Fast Fill Lever. It is in-line after the cold water line open/close valve & before the expansion tank. The fast fill lever offers no resistance when I put it in the "fast fill" (up) position, though in the past there had been slight resistance. Is that perhaps indicative of a bad fill valve?
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    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
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    #10

    Nov 27, 2009, 01:34 PM
    Well 12 PSI is not enough to cause the 30 PSI safety valve to pop so it is eighter a bad gauge that is not showing the correct system pressure since if it was 12 PSI or the new safety valve is defective and opening at 12 PSI. If it were me I would hook a test gauge on the 3/4 inch hose bib connection that is usually installed to drain the system down and see exactly what the system pressure really is. Then if that checks out then the new safety pop off valve could be defective but that would be rare for a new valve unless someone played with it..
    tk03's Avatar
    tk03 Posts: 33, Reputation: 2
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    #11

    Nov 28, 2009, 11:05 AM

    If there is no resistance I think you have a bad fill valve and the Gage does not work. There is no resistance when the pressure is real low but when it starts to get close it will encounter resistance to lifting.
    I would replace the gage if the pressure does not drop when you had the tank drained.

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