Boiler harmonics/piping fix

I'm still confused. You say "three pump system" and then you reference four pumps: one for each zone (3), one for the boiler (in the boiler?) and one for the secondary "building loop".

From the above, however, may I suppose that you only hear the noise when the boiler (internal) pump is running, but always hear it when that one pump is running? Is there any way you can run that one pump without the boiler firing? And are there any valves on that particular circuit?

And how does that pump relate to the secondary "building loop" pump.?

Videos have to be hosted elsewhere and the link posted here.

I haven't posted lately because I felt insulted. My nature is to be helpful & hopeful rather than hurtful. Kinda like Ed. But, I felt compelled to address this post.

Eric, I have, in any installation, rules that I always try to follow. The supply piping into any pump, 10 to 12 pipe diameters of straight pipe and 5 pipe diameters of straight pipe on the output of the pump before any directional change in flow. Common Manifold piping should be generously sized. ( I don't know whether yours is 1" or 1 1/4". You have 3 zones of 3/4" pipe at 4 GPM for 12 GPM when all zones are operating. The Common Manifold piping should be sized for that.) The Extank should be on the imput to the pump(s). Yours appears to be. I always pump into the highest pressure loss in a circuit. The Air Eliminator should be on the hottest water from the boiler. Yours is kinda iffy. There are more rules, but let me say that I like an install to be as aesthetically pleasing and symmetrical and minimal as possible. Yours, Eric, is not. Let's address the Delta T.

The Delta T is not sacrosanct, but it does indicate how a system is functioning. A 10 deg Delta T can lead to short cycling of the boiler and a 50 deg Delta T can indicated an undersized boiler, excessively long heat emitters, an excessively high heat exchange rate to the environment, etc. This is my thinking on your sys as to the Delta T. (The reason for a bypass valve is to prevent or minimize boiler condensation. All boilers condense at some point in the heating cycle. The idea is to prevent sustained condensation which is destructive to the flue and boiler heat exchanger.) The boiler bypass valve between the input and the output of the boiler is a ball valve. It appears to me to be 1" piping and valve. This means that the valve would have to be 97% closed to provide any real regulation. Aside that, a ball valve is a poor choice for bypass valve. You would have been better off with a 1/2" pipe and 1/2" ball valve as it would have given you better regulation. I prefer a Caleffi boiler bypass valve and I have used with great success a Taco I- Series modulating valve with sensor set at 135 degs.

Mixing the hot water from the boiler output to the boiler input will lower the Delta T. What is helping lower the Delta T, also, I think that the Grundfos pump in the common manifold piping. I DO NOT think that that pump is necessary and I would remove it as your diagram shows. I have used your diagram many times and would only change the location of the pump. Per my rules, I would pump into the boiler not away. I do not know the BTU rating of your boiler, but for every 10,000 BTUs you need 1 GPM thru the boiler. So, size the boiler pump on the flow you need to over come the pressure loss of the boiler circuit, which I would think is pretty minimal. Look at the Grundfos UPS26-99FC 3 speed flow chart and select the GPM you need at the pressure loss and select the proper speed or maybe a different pump. One last thing before I close this comment.

As the boiler reaches 170 deg when the harmonics start, close the bypass valve and see if that makes a difference and measure the Delta T. Also, I would put balancing valves on the output zone piping to the Common Manifold and set them to about 4GPM. This would balance out your 3 circuits so that the greatest flow wouldn't be going thru the shortest circuit. I like Caleffi Quick Setter balancing valves.

https://www.supplyhouse.com/Caleffi-132552A-3-4-NPT-QuickSetter-Balancing-Valve-w-Flow-Meter

I have use a mechanic's stethoscope you can get at Harbor Freight or any auto parts store and checked the sys. It is helpful in pinpointing noisy components. Or, Amazon's

allsun Auto ultrasonic Car Noise Finder Diagnostic Listening Device Stethoscope 100Hz-10kHz Black. Or,

Chassis Ear Automotive Engine Noise Finder Tool, 6 Channel Chassis Ears Sound Detector Identify the Troubling Engine Noises (Over-Ear Headphones)

Noise is not necessarily a harmonic. Harmonic has a specific definition.

What is the model of the 3 Taco zone pumps. Are the Taco pumps multi speed? The 2 Grundfos UPS 26 are UPS26-99FC , I guess. What is the size of pipe in the common manifold piping? I find it difficult to understand why a properly sized Taco zone pump can not circulate water thru the zones and the common piping. Perhaps, the common piping Grundfos UPS 26 is adding a pressure increase to the Taco pumps, increasing the flow thru the heat emitters giving a lower return temp to the boiler. When you say, "When I disconnect the wiring from the pump on the common piping the heat doesn’t travel through the common piping causing the boiler to over heat and not work at all" What do you mean by 'over heat' and 'not work at all'? I assume that the boiler pump is working and that the boiler water temp has reached the set temp of the boiler (not high limit) and stops firing for a length of time allowing the boiler water to cool down to the re-ignition temp. This can be because there isn't flow or insufficient flow thru the heat emitters which would release the heat energy into the environment returning cooler water to the boiler. Are all your gate valves on the supply/return fully open?

Are you getting sufficient heat from your zones? How many thermostats do you have?

I'm not enamored with the B&G flow control valves. You might try this—Flo-Control Valves are designed with a handle on top that when turned fully counterclock-wise will permit gravity circulation (open up).

Try the stethoscope thing and try and pinpoint the noise.

Yes, I have dealt with harmonics on the copper heat exchangers. all on horizontal flow models and it has been that the heat exchanger has been internally scaled inside. It does become more pronounced has the loop temperature starts to rise. I would question how you descaled the unit. Did you make sure that the descaling solution is going thru the heat exchanger, not thru the system. You will need roughly 1-2 hours to properly descale. its a hard thing to troubleshoot because if you shut the gas valve off it tends to go away and you cant just shut the boiler pump off as you will flash to steam. I know you said you flushed it, but did you use descaling solution or vinegar? I would do it again.

the only other thing I have found causing harmonics at high decibal level is bad combustion. I normally find those on mod/cons as the air/ratio is out of wack from high fire to low fire. have checked the combustion?

The piping as is is mostly fine. The system is set up as primary/secondary with injection and bypass for boiler condensation protection. This means that bypass valve by the boiler should be somewhat open not fully closed. You want to adjust that so that when the zones are running the return water to the boiler stays above 130F. The closed space Ts (boiler and zones) and such are fine as long as the flow directions are all correct, hard to see that form the picture but you sketch the actual setup including pump directions you can see if it is right.

If you want to re-pipe, your diagram is meant for modcons and won't work* as you'll lose the boiler bypass.

As for the noise, I would vote for cavitation from low system pressure. This would only show up when the boiler is hot.

*you can make it work but you have to watch secondary primary flow rates. Secondoary flow rate has to be well bellow primary. A better option is Fig21 here:

https://www.weil-mclain.com/sites/default/files/field-file/cgi-4e-series-2-manual_1.pdf

The installation manual answers most of your questions. 1-1/2" piping at the boiler is adequate up to the 400K unit

You could run that boiler out to a 30∆ which would require 19 gpm. Well within that circulators capacity. Very low pressure drop thru that boiler even at a 20∆, 28 gpm flow

Regardless if you pump into or out of the boiler the gpm will be the same. With the short piping loop I suspect you are flowing over 20 gpm on speed 3. I'd adjust the boiler pump speed based on the delta across the boiler. Probably end up between 20 and 30 ∆

Looks to me like you are pumping into the boiler, unless this pump is backwards?

The boiler pump is referencing the PONPC, the expansion tank connection, via the closely spaced tees (hydraulic separation).

You could move the tank right at the boiler pump, then all that pumps ∆P shows up in the boiler. With caution as high head circs can sometimes cause the relief to seep if the dynamic pressure approaches 30 psi. Currently the boiler circ "sees" the expansion tank through the close tees. I doubt the change would change the boilers operating pressure much.

The advice above to boost the static fill to say 20 psi, does the noise stop? Then high temperature low pressure could be inducing some cavitation. Although pumps don't last long under that condition. Could be the impeller has been chewed away in the boiler circ. Easy enough to pull and check the boiler circ impeller.

180F at 10- 12 psi is not a cavitation risk at all. Again, a gauge on the boiler will confirm the dynamic (flowing) pressure.

Confirm that you have an accurate pressure gauge. A gauge in the boiler will show you static fill and what the pressure increases to when the boiler circ runs. Easy enough to remove the relief, put in a tee and add a 30 psi gauge to confirm. Or on a boiler drain.

Do some more troubleshooting before you breakout the sawzall and spend $$ and not arrive at a fix.

Add up the fin tube lengths to arrive at the btu that can actually be delivered, regardless of how large the boiler is. I'd be curious what the smallest zone come up at.

Copper fin tube boilers are basically a flat copper fin coil, not unlike an AC coil. Two headers with 5/8" finned copper tube going across.

There really isn't a low point. Here is the RBI he has. Generally with the correct pump, as he has, the flow velocity keeps them pretty clean. 20- 25 gpm flowing thru 8 or so short 5/8" copper tubes.

DHW copper tube boilers tend to scale as they see fresh water constantly. Unless this system has a leak or gets flushed often, the water hasn't changed too much.

Odd is it made the noise from day one?

They don't usually ship from the factory with scaled coils :)

Any possibility you are low on water?? We had a situation with this exact type of boiler earlier this winter that whenever the burners where on there was a very strange high pitch noise that could be heard throughout the home. The gauge showed 15psi which we found was stuck when we drained the system.

Repiping might not fix the problem. I would root cause the issue and fix from there, throwing more pipe at the problem won't help.

While there, fire the boiler so it gets up to temp where it starts to sing. Turn off all pumps and turn each pump on one at a time to see which loop is creating the noise. If you isolate to a single pump, try adjusting the flow on the pump, either by changing its speed or by throttling the outlet, to see if it effects the noise.

Once you know the problem, it might be a simple fix.