Intermittent Grundfos noise

DIYChris

I have an infloor radiant system (built by the original homeowner -- a plumber -- nearly twenty years ago); the boiler and pumps are located in the basement and the house is two-story.



The primary loop uses two UP26-99F Grundfos pumps in series feeding four loops, each controlled with zone valves.



In the last year or so, I have noticed that the trailing pump sometimes buzzes: I may not have it completetly sorted out, but the buzzing seems to occur when the pressure drop across the pumps is low (a delta P of 5 psig or lower, i.e., multiple zones open/high flow) and/or the system is cold and heating up (i.e., the water temp going into the pumps is 90-95F or less). Eventually the buzz goes away after the system has been running for a while.



I am thinking that the pump is probably starting to go but thought I would ask the experts.



If the pump is going, is there a repair kit or am I better off just replacing it?



Thanks!

furnacefigher15

Yes and no

Most cartridge pumps have replacement cartridges available, but I've found that to be touch and go.



I think it's best to just replace the whole pump.

Mark Eatherton

Seriously???

2 2699's in series? What the heck kind of tubing do you have? 1/4" PEX, or maybe 3/16" rubber?



The cost of a replacement cartridge for that pump is more than a whole new pump. You make the decision :-)



But I'd much rather see if you can get by with either one pump, or possibly a variable speed pump.



ME

furnacefigher15

Mark

I imagine it has more to do with the length of the loops, then with the size of the tubing.



Also it was probably cheaper to buy 2 smaller pumps, then 1 big one.

Mark Eatherton

Well....

In my 35 + years of experience, I've seen three apps where it required 2699's in series.



One was a radiant floor project with a 1,000 foot loop length, and the other two were BESI rubber radiant jobs.



Let's see what the consumer says.



2699's are NOT a small pump as it pertains to residential/light commercial systems. 850 watts each if memory serves me correctly. Here in Denver, that would be $0.17/hour for the two of them.



ME

Alan (California Radiant) Forbes

It's more like

205 watts, but still very high, especially if you don't need a 25-30 foot high pressure drop.



http://www.us.grundfos.com/web/download.nsf/Pages/CB0DD920244366288825650C0067D3BC/$File/L-UP-TL-107.PDF



As far as the buzzing noise, you usually hear that on a device that has a relay or transformer, not a pump.  But since the pump vibrates, there might be something inside that is loose and makes a noise when the pump is on, albeit at different loads.  I'd say not to worry about it unless you can hear it in the living space.  If so, replace them pump, perhaps with one correctly sized.

DIYChris

Thanks for the feedback!

Thanks to all of you for your feedback.



Per pump sizing, as I did not design the system, I can't really comment. Primary loop is 1 1/4" copper on the discharge and intake. There are actually six total loops: Four have zone valves (distribution headers at each location are three, five, six and eight loops --- no idea on tubing lengths) and two loops are open all the time (250' each), presumably as cheap bypasses.



(At one point, I believe the guy was trying to use the condensing boiler to run DHW but eventually gave up. However, he left the indirect tank in place. I pitched the indirect tank and converted to a primary/secondary loop system, figuring it was more efficient and I could run the boiler at a lower, more efficient temperature.)



Sounds like pump replacement is the best option once it becomes too annoying.

Mark Eatherton

A condensor from 20 years ago???

If its a Hydropulse, that statement makes sense.



If you could show us the near boiler piping we MIGHT be able to help you select a properly sized pump.



We'd need to know the following;



Pipe size in diameter, and total length per circuit, along with an approximation of the elbows in the circuit.



Linear feet of baseboard connected to each circuit.



As a rough, quick check, we could use the total linear feet of baseboard, and the square footage of heated spaces. This is to determine how oversized the system is.



ME

DIYChris

Additional info....

At this point, I don't know that there is much I can (or want to) do to my system (other than take out one of the UP26-99F pumps in my primary loop), but since you asked....



I have a Monitor Products MZ40C two-stage condensing boiler (142,000 BTU; circa 1996) in my basement. My two-story house with basement is 5500 sq ft plus a heated garage (~600 sq ft). I have two uncontrolled zones (cheap bypass(?) with 250' loops tacked up to the underside of the first floor) and four controlled zones (all embedded in Gypcrete; range from three [garage] to seven [first floor] loops off of their respective distributors). I did not install the system --- came with the house we bought, so I could not tell you tubing length or other details. I run in a primary/secondary loop configuration.



As a point of reference (or interest), the boiler recirculating pump (Grundfos UPS15-42F set to speed 3; 17 gpm max at zero head) pumps a bit slower than the two UP26-99Fs when the second floor, five loop zone is on plus the two (pinched back) bypass loops. When I had some junk in my Y-trap last season, I was actually getting a bit of back mixing. Hence, I suspect some flow restriction in the primary loop.



Anyway, thanks for all the help and advice. Think I will soldier on from here.