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Very short cycling boiler and circulation pumps

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grrrdot
grrrdot Member Posts: 10
in Gas Heating
Hi,
Just getting settled in my "new" ( to me ) house. A week or so ago the boiler stopped with an error about low flow. The main circulator is a three speed pump that was set to low so I moved it up to high to try and buy some time.
With the pump on high and a call for only hot water the boiler does not error but it cycles rapidly, as in on and off twice in 2min.
I can hear the circulator pump running and it makes a little rattling noise, not good. I tried bleeding the system thinking it could be air lock but it did not make a difference.
When the boiler fires the water temperature gauge moves up until it reaches temp the boiler shuts off then the temperature quickly moves back down again. Here's a video I made of it cycling: https://m.youtube.com/watch?v=a1pQaFgxL2ghttps://m.youtube.com/watch?v=a1pQaFgxL2g

So this has me feeling like maybe the main circulator pump is bad and not flowing enough water. I started poking around to understand the pump that's in there and I'm not sure if I am doing this all correctly:

Here is a diagram of the entire system: https://i.imgur.com/n7bnwU2.pnghttps://i.imgur.com/n7bnwU2.png
Boiler's head loss curve: https://i.imgur.com/kHMvz4z.pnghttps://i.imgur.com/kHMvz4z.png
Hot water tank stats: https://i.imgur.com/fDy2UKa.pnghttps://i.imgur.com/fDy2UKa.png
Circulator pump curve: https://i.imgur.com/R0aiBUp.pnghttps://i.imgur.com/R0aiBUp.png

Seems like I need at least 8GPM for the 1.25" copper and the water tank recommends 8GPM as well.
Water tank literature says at 8GPM there's 6ft of head, if I read the boiler curve right it says at 8GPM is ~7.5ft and there is 10ft of 1.25 copper pipe so that's ~.5ft. of head.
Looking at the current pump's curve I don't see how this could ever have moved 8GPM with a 14ft head.

The piping for this system is different than what I have seen before am I doing something wrong or is this pump just to small?

-G

Comments

  • Ironman
    Ironman Member Posts: 7,376
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    I'd take the motor off of the volute at the 4 Allen screws and see if there's some debris in the impeller (isolated the pump from the system first).

    It looks from the numbers that a 15-58 is too small. It should have been a 26-99 like what's going to the rad's.

    In all honesty, if that boiler has that much head, it should have been piped primary/secondary.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • grrrdot
    grrrdot Member Posts: 10
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    OK,
    So I swapped the UPS 26-99 circulator into the main loop and on medium speed the boiler cycles much less frequently. BUT, if one floor of the radiant floor system calls for heat and at the same time the top floor radiators call for heat something happens and the radiant floor gets zero flow from the main loop and just cools off.
    If I turn the main circulator to low the boiler cycles more quickly but it seems like everything gets heat.
    So, not sure whats happening here I didn't think it mattered what speed or type of pump the main circulator was.
    When I look at other systems the secondary supply and return lines are not spaced out on either side of the main circulator like this but other systems I've found don't go through the water heater either.
    Is there something wrong with the piping layout?
    https://i.imgur.com/n7bnwU2.png
    -G
  • Ironman
    Ironman Member Posts: 7,376
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    Is the circulator for the indirect running when any of the space heating circs are running?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • grrrdot
    grrrdot Member Posts: 10
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    Yup, that's how its all wired. Indirect circulator kicks on when anything in the house calls for heat.
    I think it needs to run to get enough flow through the boiler.
    -G
  • SeymourCates
    SeymourCates Member Posts: 162
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    @grrrdot

    Here is the installation manual for your boiler:
    http://support.noritz.com/download.php?file=Literature Page/Installation Manual/NH IM.PDF&field=InstallationManual

    Look at page 20.

    This is the proper p/s piping arrangement that is required. Yours was piped by a creative genius that never bothered to look at the manual. Until it is piped properly, all of the zones will continue to affect each other depending on which is running at the time.

    Furthermore, the boiler is a poor choice for a heating application as it can only modulate down to 50K. Short cycling is inevitable as it is impossible to dump 50K into such a small building unless all zones call simultaneously (and even in that situation it is doubtful under steady state conditions).
    Zman
  • Ironman
    Ironman Member Posts: 7,376
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    SeymourCates said:

    @grrrdot

    Here is the installation manual for your boiler:
    http://support.noritz.com/download.php?file=Literature Page/Installation Manual/NH IM.PDF&field=InstallationManual

    Look at page 20.

    This is the proper p/s piping arrangement that is required. Yours was piped by a creative genius that never bothered to look at the manual. Until it is piped properly, all of the zones will continue to affect each other depending on which is running at the time.

    Furthermore, the boiler is a poor choice for a heating application as it can only modulate down to 50K. Short cycling is inevitable as it is impossible to dump 50K into such a small building unless all zones call simultaneously (and even in that situation it is doubtful under steady state conditions).

    That's probably why it's piped like that. It's using the indirect as a buffer tank, which would be okay if the secondary connections were correct. As it is now, the secondary circs are fighting with the primary to achieve flow.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • SeymourCates
    SeymourCates Member Posts: 162
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    The buffer tank holds 20g. Presume the tank is satisfied and standing at 130F. Assume the maximum effective tank temp that can be attained is 170F (poor transfer as tank approaches SWT). 6400 BTUH maximum dump capability.

    Useless on a 50K boiler.
  • grrrdot
    grrrdot Member Posts: 10
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    Thanks for the comments, super helpful!

    I'll be doing some renovation and putting an addition onto the house in about a year. Unfortunately the addition isn't enough to use 50K of heat but the whole heating system needs to be moved up a floor ( I'm in a flood zone ) so I could do a major reconfiguration then.

    In the meantime I'm wondering if I can get this more workable without completely rebooting by moving a few pipes to have more of a series setup? Like the image here: https://pmengineer.com/articles/88031-selecting-a-primary-loop-circulator-the-myths-and-the-facts

    So changing my diagram it would turn out like this: https://i.imgur.com/1rD9QBn.png

    Feels like this setup would stop the pumps from fighting each-other at the cost of the upstairs radiators seeing some temp drop from the hydronic system and both heating systems suffering if someone takes a long shower.
    ?
    -G
  • Ironman
    Ironman Member Posts: 7,376
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    That would be my recommendation for a simple fix. However, the higher temp emitters should be upstream of the floor, not downstream like you now have it.

    In your diagram, you could just move all the secondary connections straight down to the hot supply, before the buffer tank. That would put them in the correct order, but may give you a little less domestic hot water.

    The Tees for each secondary loop should be placed as close together as reasonably possible, not exceeding 12".


    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • grrrdot
    grrrdot Member Posts: 10
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    OK,
    I re-plumed as suggested using closely spaced tees off the primary loop and everything is working much better. All zones can call for heat and the system delivers without flow errors. The piping looked bad to begin with and now its even more insane but it all works!

    Thanks for the feedback from everyone its been very helpful.

    -G
    IronmanRich_49

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