I've just moved into a house with a radiant heating system, with a non-functional circulator pump (I knew this when buying the house, thinking that I would replace the pump after moving in).

The old pump was a Grundfos UP 26-99F, and I was able to order the exact same model online. After draining the system, replacing the pump, refilling it, and turning on the heat, it seems like the pump is causing an abnormal amount of noise.

I don't really have a basis for comparison, since I haven't lived with this kind of system in the past, but it's definitely not the "whisper-quiet operation" that the Grundfos manual promises. It seems like the pump is creating a slight amount of vibration that reverberates through the pipes and becomes an audible hum on both floors of the house. It's actually more loud on the first floor than it is directly at the pump (in the basement)!

My question is: is this normal? If so, are there ways of dampening the noise a bit? And if not, what can be causing it? I'm fairly certain that the pump is indeed moving water as intended, and everything else in the system (temperature, pressure) is fine.

  • Was the air purged from the system?
    – Ed Beal
    Commented Nov 20, 2016 at 8:24
  • Yes, I'm pretty sure all the air is out. (Wouldn't that be a different noise, though? Mine is a very uniform humming) Commented Nov 20, 2016 at 13:15

1 Answer 1


I got it! After some more research, it seemed like this was the kind of noise that indicates an imbalance in the impeller. So I pulled apart the pump, and lo and behold: there was a piece of debris stuck in there. After cleaning it out, the pump really is working with "whisper" silence.

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