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Thread: Rinnai tankless popoff valve problem

  1. #1
    DIY Junior Member BrianWitty's Avatar
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    Default Rinnai tankless popoff valve problem

    Hey guys, new to the board...

    I have a rinnai tankless outdoor gas unit (the big 9.4 gpm one) anyway, it's been installed about 2 years now with no real problems. All of the sudden yesterday, I noticed a big puddle in the yard. The popoff valve was pouring water on the ground like it was a garden hose. I turned off the unit and it stopped. I pushed in the popoff felt a click, and turned it back on. Turned on the shower and had hot water, and the popoff wasn't open. Then when I turned off the water, the popoff again opened and started spilling hot water on the ground again.

    Any ideas?

  2. #2
    DIY Senior Member Reach4's Avatar
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    Failed expansion tank?
    Last edited by Reach4; 10-22-2013 at 12:13 PM.

  3. #3
    DIY Junior Member BrianWitty's Avatar
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    Mine is an outdoor unit- attached to the brick. It doesn't have the expansion tank.

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    DIY Senior Member Reach4's Avatar
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    If there is something that keeps water from feeding back to the source, and there increasingly is, you need to add an expansion tank. Was your water meter change recently? It might have added a one-way valve to prevent water from feeding back into the mains. So if your water is coming in at 70 PSI, and it gets heated by the water heater, the water expands. The larger volume of water has to go somewhere.

    I don't know if those popoff valves are made to reset just under the pressure needed to trigger them, but if there is a significant difference in the pressure.

    Of course the problem could be the popoff valve going bad and triggering at too low of a pressure or temperature.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Is that valve designed to open on temperature or pressure or both? If it's temperature, and the burner doesn't turn off when you stop using water properly (flow valve sticking?), it will continue to heat the water , causing it to get REALLY hot, that safety valve should open.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    DIY Junior Member BrianWitty's Avatar
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    I guess changing the popoff will eliminate bad popoff valve... The temp of the water coming of the valve is hot but not really hot- probably 110-115F. I don't don't if the meter was changed, I was out of the country last week and the problem showed up the day we returned.

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    DIY Senior Member Reach4's Avatar
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    I would measure the water pressure. http://www.homedepot.com/p/Watts-3-4...IWTG/100175467

    Pressure or heat should open the valve. I think you may need an expansion tank, which could be indoors.

  8. #8
    DIY Junior Member BrianWitty's Avatar
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    Ok - certainly not opposed to an expansion tank. I did however do another test- I turned the shower on and left it going for about 15 minutes. I went outside to check before shutting the water off and the popoff was open again. Temperature was typical - 115 or so... I think I'll try just a new popoff valve first... Also noticed no change in the water pressure in the shower and the water coming from the popoff did not change significantly after shutting off the shower. Water was not shooting out, just kind of running out. The popoff also was not all the way open, pulling the lever increased the flow quite a bit.

    Cutting power to the heater immidiately stops flow.

  9. #9
    DIY Senior Member Reach4's Avatar
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    Quote Originally Posted by BrianWitty View Post
    Ok - certainly not opposed to an expansion tank. I did however do another test- I turned the shower on and left it going for about 15 minutes. I went outside to check before shutting the water off and the popoff was open again. Temperature was typical - 115 or so...
    I agree. That was a good test.

  10. #10
    DIY Junior Member BrianWitty's Avatar
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    Problem solved: failed Watts #40 popoff valve. Kinda pissed that an $81 popoff valve failed in just shy of 2 years... Things just aren't made with quality in mind anymore.....

  11. #11
    Moderator & Master Plumber hj's Avatar
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    The valve should NOT open on temperature rise because the burner should only operate while water is flowing through the heater, but if the valve has weakened, then you are in a "Catch-22", because the valve will open to release the excess temperature, but the water flowing out of it will continue to keep the burner running and the water hot, therefore the valve will never close.
    Licensed residential and commercial plumber

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