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Pressure up with new circulator

Toad Member Posts: 14
Originally ran a Taco 110 Red Baron. System ran at 20-25 psi. Worked well but replaced it preemptively due to age when doing other work on the Weil McLain CGA boiler (204,000 btu output).

System feeds older, larger diameter pipe and mix of cast iron radiators and cast iron baseboard on 1st, 2nd and 3rd floors above.

Pros initially selected NRF-22 as replacement. This did not circulate sufficiently to heat radiators on 3rd floor. Next tried NRF-36. On low speed, same 3rd floor issue. On higher speed, higher pitched humming set up in pipes in parts of the house and pressure in system rose well above 30psi. (PRV did not release however.) Removed some water/lowered pressure but then 3rd floor circulation issue returned. Most recently swapped for Grundfos 26-99 on middle speed. Seems to be working but at cold psi of 16 and then at 30-31psi a couple of hours after startup at 170 degrees. (Note- still no PRV release even with new 30psi/535,000 btu PRV installed.)

Is this pressure ok?

Any way to reduce pressure without reverting to 3rd floor issues?

Thoughts on PRV not ever releasing, even when psi at 35+

Is it possible that the original “flat curve pump” was able to circulate sufficient flow through system with less water/lower pressure than these higher head circulators (given lower resistance of older large pipes and radiators)?

Should I be looking to go back to a Taco 110 or B&G 100 and is this likely to address the issue? Versus exploring a larger expansion tank, etc.



  • hot_rod
    hot_rod Member Posts: 22,467
    Curious why they didn't replace with a like sized circulator. if the previous one worked fine?? The circulator just moves the water thru the piping, it doesn't lift it to the top floor, the fill pressure does that. On large pipe systems it doesn't usually require a lot of pumping power.

    Or it could be an air lock due to a drain down
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Toad
    Toad Member Posts: 14
    I have asked that question multiple times throughout this process. Response has basically been that the other pumps’ sealed design (versus need to be oiled) is improved technology and selected pumps are appropriate for the job - except they don’t seem to be....

  • mark schofield
    mark schofield Member Posts: 153
    expansion tank?
  • hot_rod
    hot_rod Member Posts: 22,467
    I agree a wet rotor circulator is a better choice, but the spec needs to match close.

    I'd th k you are over pumping, should be noise, but it should still flow all the radiators.

    If I were a betting man, and I am, I would look for an air problem. Big pipes can be a bit tough to purge especially without high point air vents,

    See Gordo post on purging radiators.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie Hall
    Jamie Hall Member Posts: 23,635

    Where, exactly, is the expansion tank located in relation to the inlet side of the pump?

    Where is the pressure gauge located in relation to the inlet side of the pump? It should be close to the expansion tank, which should be close to, but not at, the inlet to the pump, which should be close to the water feed from your domestic water.

    Has anyone checked the expansion tank? It is clearly not doing its job, and may be failed -- waterlogged. Or if it is trying to do its job, it simply isn't big enough.

    Which is sort of an answer to are the pressures OK? No, they're not.

    First off, if the pressure really got to well over 30 psi, the relief valve should have opened. If it didn't, you have not just a problem, but a major safety issue which needs to be resolved yesterday, if not before. Is there any chance it might be valved off (there should never, ever be a valve between it and the boiler, nor after it and its outlet)?

    Second, you don't need that much pressure to get water up to the third floor. If I am generous and give you 10 foot floor to height, you need no more than 15 psi to get there. The 20 psi before you changed out the pump was fine. Your cold pressure now is reasonable. Your hot pressure isn't.

    Has the system been thoroughly purged of air after you worked on it? Purging large diameter pipes and cast iron radiators isn't just a matter of opening the air bleed on the radiator.

    The original pump was probably fine. There isn't that much pressure loss to be overcome in a system with large pipes and cast iron radiators, so a high head pump is not what is required. Keep in mind that it is the cold static pressure -- set by the expansion tank -- that ensures that the system is full of water and stays that way. All the pump has to do is move the water around inside the system, and it doesn't care how many floors there are.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Zman
    Zman Member Posts: 7,605
    As Jamie indicated, the pressure question really has more to do with the location of the gauge as well as the expansion tank. If you are pumping away from the expansion tank and the gauge is after the circ, that would explain the higher pressure.
    My guess on your flow issue is that you have so little resistance in your system that the water just keeps taking short cuts and neglecting the 3rd floor. With high flow/low head circs you are moving so much water that some eventually gets everywhere. The right way to fix it is to install balancing valves (or trv's) then size the circ for the required flows. This is often easier said than done.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Dave H_2
    Dave H_2 Member Posts: 558
    I agree on updating to a wet rotor circ, and other comments about the system but those that have been used are no where near the performance you had before.

    The previous circ was a low head, high flow circulator.

    All three new circs put into your system are high head, lower flow circs. Totally different performance curves.

    The better replacement performance-wise and being a wet rotor design would be the 0010 or the 0010 three speed.

    Dave H.

    Dave H