We have a Grundfos UP15-29SU circulator pump that serves multiple units and is making a high pitched whine. Is that normal? Do you think its locked up and I need to remove the cartridge? Or do you think I should just replace the pump. I've attached some pictures for reference. image of Grundfos UP15-29SU

Picture of Water Heater Closet

  • tie those coper lines to the wall to reduce vibration
    – Traveler
    Commented Dec 10, 2022 at 3:04
  • Note that these pumps are somewhat expensive but you can replace many parts such as bearings that might be the issue here for a lot less money.
    – jwh20
    Commented Dec 10, 2022 at 12:48

2 Answers 2


A very simple, first try would be to open the big center screw/plug which seals the ring gap between stator and rotor. Caution, the water can be very hot. Skin protection is necessary, if the water is above 50°C. A tray or small basket should catch the tiny amount of water which will flow out. Important since the water can be very dirty.

The pump should be switched off before removing that screw/plug. And the system pressure should be read.

If open, the pump can be switched on for 10 or 20 seconds or a minute.

The relaesed water hopefully will wash dirt and small metal or lime particles out of that ring gap which can be the cause for the unusual noise.

This screw/plug is specially made for this simple maintenance.

After remounting the screw/plug, the pressure of the system has to be checked. Water should be refilled, if the pressure was decreased. But sometimes, only demineralized or treated water is approved by the system's manufacturer.

In case of a total blockage, the rotor shaft (which is only accessible after removing the screw/plug) can be manually turned free with the help of the very same screwdriver which opened that plug/screw.

A second possible cause for unusual noise or/and reduced power of the pump is a capacitor with decreased capacitance in the electric connection box. Could be checked by an electrician via an electronic test device for capacitors, which is sometimes part of a multimeter.

Normally those type of pumps are very robust, undestroyable and reliable, if the maintenance points described above are checked every few years (ring gap cleaning and capacitor value).

Sometimes a filter needs to be installed (incl. a magnet to catch all rust particles), if the water is too dirty.


They should be almost silent.

Making a whine means something is wrong. Would at least take it apart to see. Might just be sediment blocking the pump or a bearing going bad.

It is nicer if shut off valves are place before and after.

If whine has been going for a long time, replacement might be needed.

Turn off power before work.

  • 2
    I'm thinking bearing.
    – JACK
    Commented Dec 10, 2022 at 1:21

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