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Thread: water heater venting water outside from what I think is mixer valve

  1. #1
    DIY Junior Member montags's Avatar
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    Default water heater venting water outside from what I think is mixer valve

    Hi,

    I have a gas powered water heater tank that is continually leaking hot water outside via what I think is an overfill pipe. Having looked at diagrams online, I think it is coming from what is called the mixer valve (please see photos below). I originally thought it was coming from the pressure relief valve (PRV), but that is a separate plastic pipe and is not leaking. Note that I have two vent pipes to outside, one from the PRV and a second from this "mixer valve" thing.

    I did test the pressure relief valve and it seems to be working fine. Flows when I open it and stops when closed. When I do operate the PRV, the venting of water from the "mixer valve" stops for a minute then starts dripping again. It is a vigorous drip, maybe a few gallons per day. We have no complaints about the volume or temperature of our hot water.

    The water heater is 13 years old and despite having the manual, I do not know what manufacturer it is. There is no ID on the manual, not even a name. We live in a soft water area and this heater is the original install on 1999 house. Note that there is a continual ssshhhh sound like a faucet is running and it is coming from this valve.

    I was hoping it was an issue with the PRV and maybe it is - I know little about water heaters.

    Thanks for any help.

    http://mcontact.bestmail.us/DSC_0475_new.jpg

    http://mcontact.bestmail.us/DSC_0471_new.jpg

    http://mcontact.bestmail.us/DSC_0474_new.jpg

    Valve in question:
    http://mcontact.bestmail.us/DSC_0478_new.jpg

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    The valve on the side tank is a T&P valve - the fact you can open it is no perfect indication that it's good.

    A mixing valve would require both the hot and cold to connect to it (it's called a tempering valve). I'm not sure, but I think it's a pressure relief valve (again, not a PRV). It could be defective, or could be doing its thing...it would normally be set lower than when the T&P opens. If you have an expansion tank, it could be shot. The city could have raised the supply pressure (new pump, or new water tower, for example).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member montags's Avatar
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    Thank you Jim. Those are all good, well thought out points. I can see you are an engineer, so that makes sense. I think you are right, it is a pressure relief valve. I am in two minds about just replacing it because as you hinted, there could be other problems and it's just a symptom.
    Last edited by montags; 09-30-2012 at 08:26 PM. Reason: missing word

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    Plumber jimbo's Avatar
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    I would investigate WHY someone, at some point, thought it necessary to install a seconday pressure relief valve. Check you system pressure both static ( no water running) and dynamic ( a faucet open)

  5. #5
    DIY Junior Member montags's Avatar
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    Quote Originally Posted by jimbo View Post
    I would investigate WHY someone, at some point, thought it necessary to install a seconday pressure relief valve. Check you system pressure both static ( no water running) and dynamic ( a faucet open)
    Thanks Jimbo. Good points. I'll raise this when the plumber is looking at it.

  6. #6
    Forum Admin, Expert Plumber Terry's Avatar
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    It looks to be an extra valve there.
    Some areas required a relief line on the main piping, and none on the water heater. A dumb idea maybe, but that's what some inspectors wanted. Some were done because there was no way to drain a relief off the heater. We could position the relief high enough to get a good gravity drainage off the relief. Since the T&P is being drained outside, it would seem that the one higher up could be deleted.

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