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My Grundfos UPS15-58FC has become a bit noisy when operational. Its a part of my heating system and it starts to hum from time to time and this causes the pipe its on to vibrate. I would like to try and bleed the air out of it. Correct me if I’m wrong but this seems to be the way to go with circulating pumps. Is it possible to bleed the air out of it? It seems to have plastic covering where the pump bleed screw would normally be and it says “With Check Valve”…I’m a bit lost - I was expecting a pump bleed screw and I’m not sure I see how a check valve prevents air from building up from the inlet. Can somebody please shed some light? I’m afraid of trying to pry out the plastic cover - it seems to be on very tight - in case that breaks the thing.


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I found a manual bleed valve at the top of my water loop and I slowly turned the small nob on the side until a bit of water came out (circled at the top right), then screwed it back in. I also ran some hot water through the pump by opening the red valve (circled at the bottom left) which rests under the Grundfos (arrow points to the Grundfos). Will report back in a few days, or if anyone else has more suggestions, please feel free!

  • 4
    you probably have to bleed some nearby pipe. how is your pump installed?
    – Jasen
    Commented Nov 2, 2021 at 23:42
  • @Jasen Its connected to the hot water pipe. Water flows down in this pipe. The inlet at the top of the unit has a shut-off valve located above the unit. The outlet at the bottom of the unit also has a shut-off valve located below the unit. Beyond the shut-off valve there is a drain valve on the pipe. Should I shut the top valve off and then open that drain with the bottom valve open?
    – Alexandru
    Commented Nov 3, 2021 at 12:48
  • I've never seen a circulator with a bleed valve, and never seen or heard of anyone bleeding one. I did just now watch the youtube video that you probably have, of someone bleeding air out of a pump similar to the one in your picture, except that one has a screw and yours doesn't. I'm mystified as to why it would be necessary. Maybe if the circulator is installed horizontally with the motor housing facing upwards??? But if it's installed as in your picture, the bleed valve would need to be somewhere above it in the pipework.
    – jay613
    Commented Nov 3, 2021 at 14:18
  • No. The opposite. When you bleed the system the air needs to be replaced with water. The water supply needs to be on and the water pressure, from it, needs to be high enough to push air out of the highest point in the system. (Top of the highest radiator). Otherwise it won't bleed.
    – jay613
    Commented Nov 3, 2021 at 15:52
  • @jay613 I’ve edited the question and added what I’ve done so far along with a picture of the setup. Please let me know if that sounds okay!
    – Alexandru
    Commented Nov 5, 2021 at 0:48

2 Answers 2


Air vents in hot water circulation systems are, or should be, located at high points (sometimes local high points) in the system. They are pretty much never right at the pump, in my experience.

Depending where the hot water loop runs, the appropriate vents might be on the other side of the house, or two stories above the pump. There is usually one near the boiler, typically on top of an "air scoop" which typically has an expansion tank on its underside, but there are many variants. The rest tend to be tucked on at the highest elbows in the system, often hidden behind baseboard covers if baseboard heat, or at the high parts of hot water radiators.


I'm troubleshooting mine right now. Something wrong with the pump itself. Will likely need to replace. However, regarding your question about the plastic cover, don't worry about it. It's very tight, and removing it gives you access to nothing. The motor and pump are integral. The part that comes off is the permanent magnet electrical portion.

  • In the end, replaced all the Uponor plumbing because some parts where plumbing created peaks above the height of the rest of the PEX plumbing were trapping air. I also added an air eliminator on the cold intake of the boiler and some valves to close the HVAC loop with the expansion tank in the loop. Also realized one of my check valves were very noisy so replaced it. I think one of these many changes solved my issue. It probably wasn’t the Grundfos afterall…
    – Alexandru
    Commented Nov 6, 2022 at 4:02
  • This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
    – FreeMan
    Commented Nov 7, 2022 at 16:30

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