Author Topic: Circulator Pump rattle  (Read 3405 times)

keeper

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Circulator Pump rattle
« on: February 02, 2016, 01:40:18 PM »
First time poster here! Plumber newbie.

Recently I started hearing a rattling sound coming form my circulator pump on my hot water heating system when it was running ; sometimes. Its a simple setup, 4 zones, 1 pump. This past weekend I bled all the lines thinking air was in the lines. Verified the expansion tank is in working order as well. As I progressed I figured out that the pump only rattles if a single zone value is open. The moment two or more of the zones are open the pump is quiet as a baby (and running). I tested this several times to verify. With my limited knowledge on these systems to start go guess what is going on?

Anyone have any thoughts on this? Should I be concerened

zolotiyeruki

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Re: Circulator Pump rattle
« Reply #1 on: February 02, 2016, 02:24:52 PM »
With one zone, you'll have lower flow and presumably higher pressure at the outlet of the pump.  Maybe it's cavitating?  Or there could be a different mechanical failure inside that only starts becoming a problem when the pressure increases.

How much does a replacement pump cost?

BudgetSlasher

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Re: Circulator Pump rattle
« Reply #2 on: February 02, 2016, 05:38:48 PM »
I cannot speak to what your problem may be, but if you end up having to replace the pump, look into an ECM circulator motor rather than a split-phase (they use power more efficiently). You may also want to look into a delta-T (change in temperature) or delta-P (change in pressure) they adjust the circulator speed based on either the difference in temperature between outgoing and returning water temperature or the changes in pressure depending on how many valves are open.

I looked into them as part of an upgrade and could not justify the cost to replace a perfectly functional motor, but if one failed I would investigate again.

keeper

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Re: Circulator Pump rattle
« Reply #3 on: February 02, 2016, 06:25:42 PM »
With one zone, you'll have lower flow and presumably higher pressure at the outlet of the pump.  Maybe it's cavitating?  Or there could be a different mechanical failure inside that only starts becoming a problem when the pressure increases.

How much does a replacement pump cost?

I think you are on to something. I did not know what cavitating was until I just looked it up. It seems to line up well with what I am hearing. I am going to go down this road a bit more if for nothing else to educate myself. Thanks!

As for the cost, its a taco model, I can get a replacement for $99 on amazon. So not a deal breaker if it goes, but I have to be sure its on hand due to my climate.


keeper

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Re: Circulator Pump rattle
« Reply #4 on: February 04, 2016, 01:57:23 PM »
So I am pretty sure its the pump cavitating as was suggested. All signs point to this. Thank you. But I can't seem to resolve it. I went ahead and re-bled the lines and verified that my cold pressure was at 12 psi before starting things up. When running the boiler the gauge reads ~20psi which from my understanding it just fine. So I am out of ideas. The other aspect is that this is my third pump in 12 years. So I suspect there could be a basic system issue at hand (under sided?) as everything I read says the pumps should last decades, not 5 years.

Unless anyone else has some thoughts I think I will wait this one out and replace when the time comes (could be a few years for all I know). The plus side of this is that I didn't know anything about my heating system until all this research and I am confident I can swap out the pump when it happens.

zolotiyeruki

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Re: Circulator Pump rattle
« Reply #5 on: February 04, 2016, 06:20:06 PM »
Cavitation creates its own bubbles behind the blades of the pump impeller, and when those bubbles collapse, that's what makes noise.  I'm not sure that's what's happening--that was just one guess.  When you see 20psi, is that with only one zone running, or multiple zones? Does the pressure change when there's a different number of zones turned on?

BudgetSlasher

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Re: Circulator Pump rattle
« Reply #6 on: February 05, 2016, 05:27:52 PM »
So I am pretty sure its the pump cavitating as was suggested. All signs point to this. Thank you. But I can't seem to resolve it. I went ahead and re-bled the lines and verified that my cold pressure was at 12 psi before starting things up. When running the boiler the gauge reads ~20psi which from my understanding it just fine. So I am out of ideas. The other aspect is that this is my third pump in 12 years. So I suspect there could be a basic system issue at hand (under sided?) as everything I read says the pumps should last decades, not 5 years.

Unless anyone else has some thoughts I think I will wait this one out and replace when the time comes (could be a few years for all I know). The plus side of this is that I didn't know anything about my heating system until all this research and I am confident I can swap out the pump when it happens.

I would say 3 pumps in 12 years is a sign of a bigger problem . . . as far as I can tell (and the dust seems to agree with me) this house is on its original circulator pumps at ~26 years.

While you may wish to wait to replace the pump, I would encourage you to do two things; first research what pump you need (size, flares, connections, HP, ect) and second which features you may want (split phase vs ECM, delta-t, delta-p, ect), that way you already know the model you want when the time comes. And second, if you believe the pump is likely to fail (your history tends to point that way) consider purchasing the pump now and having it available; last year I came home from work, notice it was already negative 15 F outside and falling, I determined that a motor had failed in the heating system, and that might have stocked a replacement was closed. . . a job that I have done before in less than 30 minutes with a ~80 dollar new motor cost me much much more to have heat as the temperature again.