noisy grundfos pump

23 Jul 2007
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United Kingdom

Just completely fitted out my central heating system with a Worcester bosh 30CDI and I've notice that after 30min of the central heating being ON, the pump sounds noisy, like its got sand in it! Its a grundfos 15-60 which I bought new. It is silent when it begins, which I've tested on all three speed settings. Once it becomes noisy it can be reduced by switching it to speed setting 2. Has anyone ever encoutered this?


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You should only be running it on setting 2 anyway.

There might be air in the system. Have you bled the pump ( FAQ ) ?

Thanks guys

I think the problem has been mentioned from another posting. I've air being sucked into the system through the vent pipe. So I'm guessing my pump is constanlty circulation air, which is causing the noise. I've now got to do some re-arranging

Thanks though
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It can't and some older Worcesters (for example) expected it to be set to 3 ... Highflow 3.5 was one from memory.
Have you got TRVs everywhere? Are they shutting down after 30mins? Is there a bypass fitted?
Hi all

Just to update everyone. I changed my system pipes so that air is no longer drawn in through the vent pipe. The system is now fully bled and the pump is quieter. Also, speaking to three other engineers at work they all say that their Grudfos pumps are noisier, than other manufactures pumps that they have had on their systems.

I dont know about Grudfoss, but the Grunfoss pumps have a very hard ceramic bearing whereas the Wilo has a plastic bearing.

It would be a reasonable expectation that a rather worn Grunfoss pump might transmit more noise through its bearing than a make using a plastic bearing.

On a new pump I would be surprised if there was any significant difference in noise levels though.

Roughly how long did your system run with the new pump and the air problem?

Unfortunately, water-lubricated bearings wear VERY quickly when there's too little water around them! Your 'new' pump may have had equivalent of several years-worth of wear in a few days!
Hi Again

The "New" pump was installed in March. The air being sucked into the system has been since March as the layout of the whole system changed. Is this long enough to kill the bearing?


Pumps can suffer considerable wear in only a very few weeks if the operating conditions are wrong.

I have seen new boilers with bearings allowing 6 mm of sideways movement on the impeller after only a few weeks on a dirty system.


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