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Help me understand the correlation between boiler circulator RPM / HP / Head / Flow / System Pressure - see the particulars at the bottom.

CASE: My 1986 boiler came with Armstrong S25 circ (same as B&G 100). When the circ failed I replaced it in an emergency with the Taco 007. Now each time thermostat called for heat and the boiler kicked in I would hear 3-4 gentle pops from the boiler (within first 15 seconds, and never at other times). Someone here suggested lower head on the TACO 007 maybe the reason (24 vs 32). So I replaced the 007 with TACO 0010 (closest match to Armstrong S25). Sure enough the popping sounds are gone. But now water flow sound in pipes and rads is loud, and when the boiler heats up I am hearing a wailing sound. I can live with the water flow sound, but the wailing can be annoying. Why is the TACO 0010 causing the wailing? What part of the system can I adjust to stop it?

Cold system pressure has always been, and is now set at 12 PSI. When the boiler runs hot pressure rises to about 18 PSI.

PARTICULARS:

Cold system pressure: 12 / Height from gauge to the highest rad: 14 feet

Expansion tank: 12 PSI

Armstrong S25: 1750RPM; 1/12HP; 9-32 Flow-GPM (original system circ, was ideal setup)

TACO 007: 3250RPM; 1/25HP; 10-24 Flow-GPM (problem: few pops after boiler startup)

TACO 0010: 3250RPM; 1/8HP; 10-33 Flow-GPM (problem: water flow sound + wailing when boiler heats up)

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Roz
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  • What is the actual question, or do you want us to do your homework? – RMDman Dec 09 '22 at 21:22
  • **Why is the TACO 0010 causing the wailing?** What part of the system can I adjust to stop it? – Roz Dec 09 '22 at 23:15
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    Just a WAG, but sounds like your flow rate is too high. – SteveSh Dec 09 '22 at 23:31
  • @SteveSh what is WAG ? – Ruskes Dec 10 '22 at 03:06
  • WAG: Wild-Ass Guess. Speculation without enough evidence to support it but which might be worth checking. – keshlam Dec 10 '22 at 03:28
  • What keshlam said. A somewhat better guess would be a SWAG - Scientific Wild Ass Guess. – SteveSh Dec 10 '22 at 11:40
  • Where is the expansion tank located relative to the pump intake/output? I expect you are hearing cavitation, which is *not good.* Frequently the expansion tank is in the wrong place relative to the pump, which aggravates this. Unless you have a particularly low set safety valve, might try increasing system pressure from 12 cold to 15-20 cold, which *might* be enough to stop that, while not tripping a typical 30 PSI pressure relief safety valve when hot. put **sound of pump cavitation** into a search engine for examples. – Ecnerwal Dec 10 '22 at 15:24
  • Thanks for your replies. Definitely NOT cavitation sound. I hesitate raising pressure to test Ecnerwal's suggestion since it is already more than my home needs, by my calculation it should be good with about <10 PSI. I suspect the 0010 is too much of a circ for the system, despite roughly similar flow/head to Armstrong S25 (or B&G 100). But which specs are responsible? Velocity / horsepower? – Roz Dec 10 '22 at 19:48
  • I've gone back to 007 (prefer the few gentle pops when boiler come on to 0010's louder water flow and the moderate wailing). The 007 has lower flow than my original armstrong s25 (24 vs 32). **Is the lower flow somehow detrimental to the boiler?** – Roz Dec 10 '22 at 19:58

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