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Domestic Hot Water Recirc - rattle rattle rattle

Just completed a DIY domestic hot water recirculation system and it's working well...except for the rattle rattle. It's most noticeable at the hot water outlet pipe, but reverberates throughout the house and is most noticeable in the bathrooms. BTW, this is an 80 gallon concrete tank with a bottom cold water inlet. Questions:
  • Is it air? I don't think so, as that would ultimately come out of the faucets, right? I also don't see any bubbles in the transulucent PEX I used.
  • The tank states it has a cold water diffuser on the input, so that could potentially be the source.
Regardless of teh source, wondering about solutions. It's not the rattle at the heater that's the issue, its the fact that you can hear it elsewhere in the house, the sound transmitted via the hot water pipes.
  • I can minimize the rattle by reducing the flow with the ball valves on either side of the pump, that seems to help, but at some point that will impair the functionality, i.e. it will take a long time to distribute HW after the system turns on, or the water may cool down on its way through the system. Am I harming the pump? (Grundfos UP10-16)

  • Can I reduce the transmission of the rattle by inserting a few feet of PEX on the hot water outlet? That should minimize the sound transmission throughout the house. Does that make any sense?

    Thanks,

    Kyle

Comments

  • Jamie HallJamie Hall Member Posts: 14,906
    If you have a rattle, and the rattle is coming from or near the pump, and it changes when you throttle the flow... the pump isn't happy, and may not last all that long. Is the pump pumping into the hot water tank, sucking on the return lines? One possibility, if that is the case, is that the head loss in the return line(s) is enough that the pump is cavitating.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • KyleBHKyleBH Member Posts: 5
    Thanks, but it's coming from the hot water outlet at the top of the tank - the pipe itself. The pump is completely silent.

    The reason it reduces when I throttle the flow is that with reduced flow, whatever is causing the rattle is moving with less energy.

    I doubt I can eliminate the rattle, except for really reducing flow, or limiting its transmission somehow, perhaps with some PEX in the HW line.
  • Dave H_2Dave H_2 Member Posts: 417
    sounds like an external flow check valve. With such a small circulator and maybe too large of an external check valve can make it chatter.

    or vice versa, too small of a check and gravity flow opening and closing the check valve.

    or could be a swing check and should be a spring check......

    Dave H.
    Dave H
    rick in AlaskaGrallert
  • hot_rodhot_rod Member Posts: 14,411
    I agree with Dave, it sounds like a check valve rattle. With that small pump, I doubt you are over pumping?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie HallJamie Hall Member Posts: 14,906
    I'll third (or fourth) the check valve...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Larry WeingartenLarry Weingarten Member Posts: 2,039
    Hello, The old style heat traps, the ones with a little ball in them were great at making this noise. If it's a heat trap nipple, just replace it with a straight pipe and bend a long flex connector into a loop, so it acts (quietly) as a heat trap. :)

    Yours, Larry
    Grallert
  • KyleBHKyleBH Member Posts: 5
    I think you nailed it. From the product description:

    "The Vaughn water heater is constructed with a heat trap installed within the water heater’s hot water outlet connection. This device helps prevent heat from escaping through the storage tank’s hot water outlet during standby periods, resulting in improved operating efficiency. The heat trap is constructed from a specially designed bronze nipple with an internal floating ball that during standby periods of no flow settles and closes off the storage tank thereby preventing thermal conduction of hot water radiating through the hot water outlet."

    The heat trap is inside the envelope of the tank, within the foam insulation. So a non-serviceable design - stupid.

    Unless anyone has any brighter ideas, at this point I'm going to live with it (noise is not an issue at the heater itself), and insert a section of PEX just after the heater to minimize the transmission of the rattling throughout the HW pipes in the house.

    Thanks!
  • rick in Alaskarick in Alaska Member Posts: 1,149
    Do what Larry says and take it out. Problem gone.
    Rick
  • hot_rodhot_rod Member Posts: 14,411
    The ball should be in the nipple, and if you can remove the nipple and replace it with a plain brass (low lead :) or dielectric nipple.

    On some of those old tanks, not much of the nipple extended above the jacket, sometimes just the thread. So removing may damage the nipple.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • KyleBHKyleBH Member Posts: 5
    Just about an inch of threads protrudes above the jacket. I guess I don't care if I damage it upon removal, as long as I can install a a new one successfully.

    Seems risky though. I don't know what the other end of the nipple looks like, and if I can't get it out, and destroy the threads in the process, I'm screwed.

    I lobbed an email into the manufacturer about removing the heat trap. We'll see if I hear back.
  • hot_rodhot_rod Member Posts: 14,411
    An internal pipe removal tool or nipple extractor is another option, Or a large easy out.

    Yes it is possible to collapse that end and still not have it removed.

    I suppose a long punch could drive the ball into oblivion :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • rick in Alaskarick in Alaska Member Posts: 1,149
    If you take the nipple out ,and you have to use a pipe wrench, try and stick something inside the nipple that is as close to the same size as the nipple, like a nut driver. This will help to keep it from collapsing.
    Rick

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