Boiler pump causing rattle and hum in baseboards and air scoop

Jim100Flower

Sometimes my baseboards make a humming or rattling noise. For example, sometimes the hallway baseboard on the second floor Master Bedroom zone rattles, even when that zone is not calling for heat. Using the screwdriver listening method I found source of the vibration is the boiler pump and when I turn the speed down to low the upstairs baseboards stop rattling. However I still hear a loud hum on the first floor and the noise is loudest at the boiler air scoop. What could cause this and how do you fix it?

The boiler pump is a Grundfos UPS26-99FC (⅙ HP, max 33 gpm) that was installed new last year to replace a Taco 007 F5 that was too small for the new Laars JV225NDISU2 natural gas forced hot water boiler with six zones of baseboard and six Taco 007 F5 circulators pulling down toward the boiler. Last year both the old and the new pumps were whistling but the whistle mysteriously went away when we added Silver King Hydronic Formula No.5 corrosion inhibitor. https://forum.heatinghelp.com/discussion/169861/boiler-makes-loud-whistle-sounds-like-air-escaping-a-balloon

The pump is mounted on the input to the boiler and, although the writing on the pump is upside down, the arrow on the cast iron points down toward the boiler.

The sound does not happen every time the boiler runs, but happens several times a day. I have not been able to correlate it with a particular zone running or boiler temperature. Twice I have been in the boiler room when the boiler was cool (70F, 110F) and a zone called for heat. The boiler starts the boiler pump before it fires up and the air scoop rattle started when the pump started. That makes me think the problem is not temperature related.

Although the air scoop sounds like it is rattling, pressing against it does not stop the sound. On the other hand, pressing against a baseboard will stop the baseboard rattle. The air scoop is on the output side of the boiler.

Here's another question. What does the slot in center of the pump face plate do?

Second floor hallway baseboard rattle and hum.
https://youtu.be/DVfST9b9IyU

Boiler pump noise.
https://youtu.be/lvgOjgOQXnQ

Low speed makes the second floor baseboards stop rattling, but still hear air scoop noise.
https://youtu.be/JFmWlBCCgfo

Air scoop makes rattling noise, but I think it is coming from the boiler pump.
https://youtu.be/HZDjDh4mMhs

Ironman

How about some better pics that show all of the near boiler piping? Not close ups.

What's the cold pressure on the system?

Ironman

Also: a 26-99 should be on low speed. There's only 3.1' of head @ 18gpm on the boiler.

Jim100Flower

@Ironman here are some more pictures from last yeayr (old pump). If you tell me specific areas I can take more.
Good to hear about the low speed. The Laars manual makes a point about inadequate flow through the boiler voiding the warranty, so I thought it best to turn it up. I understand head as kind of the resistance the pump is pushing against. 3.1' does not sound like much.

Ironman

What's the cold pressure on the gauge and what's the elevation between the boiler and the highest radiator?

Jim100Flower

@Ironman Boiler pressure is steady 15 psi at all points I observed between 70F and 170F. Boiler is in basement and highest baseboard is on second level.