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Hoping for a 2nd opinion on a radiant heating system with 3 zones - only 2 seem to work at one time

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jjaslow
jjaslow Member Posts: 5
edited January 2022 in Radiant Heating
I just moved into a 50 year old home with hydronic radiant heat in the floor and have an issue I was hoping to get a 2nd opinion on. Long story short, we have a 3 zone system. Each zone has a brand new 3-speed pump and there is a 4th (also new) pump on the return side that runs when any supply pump is on. If any 1 or 2 supply pumps are running, things seem ok for those 2 zones. The floors get hot, the return pipes for those zones are around 20 degrees delta t from the outgoing pipes and the flow as shown on the Navient hot water heater is in the 1.8-2.0 gmp. But if all 3 zones are on, then one of the zones is 'dead' and the floors for that 3rd zone are cold. In fact, the pipe past the 3rd pump would be hot for appx 2-3 feet but then the pipe is cold beyond that. And the flow on the heater reads closer to 1.2-1.4 gmp. Once of the 2 'working' zones gets to temp, then that zone shuts off and the dead zone kicks back in and heats well.

The system has been described to me as an open loop, but we do have another water heater that is really used to supply the domestic heat. The valve from the radiant heater to the domestic system is closed. There is a pipe running from the city water supply that connects to the pipe coming out the water heater. Not sure why (maybe it provides the water pressure), but if I close that valve then the system ultimately fails a few days later.

Ive already paid $ to have the pumps all replaced. It did help with the system, but Im trying to get further insight on why all the zones with brand new pumps wont work properly. Thx for any help. Jason

Comments

  • Jon_blaney
    Jon_blaney Member Posts: 317
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    More pictures, closer up would help. Your piping looks wrong. Google"primary, secondary piping"
  • neilc
    neilc Member Posts: 2,707
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    what speed are the zones set to,
    and same question for circ 4 to the boiler,
    known to beat dead horses
  • neilc
    neilc Member Posts: 2,707
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    and what model is the navien?
    you say water heater, Domestic ?
    or is it a boiler
    known to beat dead horses
  • jjaslow
    jjaslow Member Posts: 5
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    neilc said:

    what speed are the zones set to,
    and same question for circ 4 to the boiler,

    Ive tried all sorts of combinations actually, none have been an obvious solution. The most common combos I use are all 4 set to high and all 4 set to medium. Ive noticed worse results if I try and vary the speeds between the zones. If I set 1 to higher then the rest it seems like all of the heat goes there.

    Usually when I go from medium to high, I see a negligible increase in the gmp, eg from 1.4 to 1.6.
  • neilc
    neilc Member Posts: 2,707
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    heater model ?
    I don't like that you have a flow rate thru heater, says it's a water heater, and wrong application,
    and you're not flowing enough thru the too restrictive heater to supply 3 zones

    try the 3 zones on low,
    and the heater on high,
    may need a stronger head circ at Bheater
    known to beat dead horses
  • jjaslow
    jjaslow Member Posts: 5
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    The water heater is a Navien NPE-210A. Probably a low end domestic water heater. I was considering having my plumber swap it out with a better heater - thats why Im glad to be getting some unbiased opinions.

    I will try the 3 on low and the return on high. thanks.
  • neilc
    neilc Member Posts: 2,707
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    ok,
    that's a flow restrictive domestic water heater, made for 30 - 80 psi well or street pressure,
    your circ might give you 20,

    you need a boiler, heating water heater,

    before you buy another Navien, google Mikey Pipes, and Navien, on Utube.
    known to beat dead horses
    Rich_49
  • Jon_blaney
    Jon_blaney Member Posts: 317
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    Took the words out of my mouth.
  • hot_rod
    hot_rod Member Posts: 22,254
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    A few mistakes with the piping. You have an attempt at primary secondary, but not quite. The supply and return tee to the various branches need to be next to one another.
    The main boiler circulator pump is not large enough to get adequate flow thru the boiler.

    I prefer the primary secondary shown below. The zones are parallel piped so they all see the same supply temperature.

    A few ways to correct this, all take some piping work.

    While not ideal for a boiler, that unit could be forced into submission.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jjaslow
    jjaslow Member Posts: 5
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    Thanks all for the advice. When I go back to my plumber, now I have some unbiased info as well.

    Final question, as you can see in my picture (top left), the pipe leaving the water heater into the pumps is also connected to the incoming cold line from the town. I assume that this is how water gets replenished into the system if needed. Maybe it also helps keep the pressure up in the pipes?

    But if I turn on the cold tap on any sink, I do notice that hot water is also drawn up into the cold pipes. Should I keep the valve open or closed? Im guessing the best is to add a check valve?

    If I keep it closed, Ive noticed that sooner or later the house gets colder. Maybe there is a leak somewhere (I dont notice one) and the water drains from the system. If I keep it open, then I sometimes get hot water instead of cold. Which is the lesser evil?