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Grundfos MQ 35 won't run

Pump only runs for a few seconds then shuts off. Turn off then back on and still only runs for a few seconds. Lots of water on supply side. Problem was intermittent but now is all the time.

Posted by Bob Martin on


1 Answer

Gil Shultz

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Sounds like the discharge is plugged. You can get the manual at:

Posted on Jun 13, 2014


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  • 1 Answer

SOURCE: Grundfos Pump Wont Stop Running

Close the outlet valve then turn electrical switch on manual for a few seconds until any air is pushed out then open the valve and return electrical switch to automatic.

Posted on Aug 01, 2010



  • 42 Answers

SOURCE: My Grundfos MQ pump won't

There should be a small cap on the motor end of the pump, take that off and you will see the stainless steel shaft with a **** in it for a flat bladed screw driver. You should not need to turn the water off. A few drops might come out, but it's safe to do it that way. Turn the shaft with the screw driver and that should loosen up the pump.

Hope this helps.

Posted on Nov 05, 2010


Hans Pearson

  • 2510 Answers

SOURCE: i have a grundfos mq

There was possibly some damage done to the pump while it was operating dry and it in now not able to deliver the required flow of water. Pumps wear very quickly when allowed to run dry, even for a short time.

Posted on Feb 19, 2011



  • 3740 Answers

SOURCE: I have a Grundfos MQ

If you have done all of that troubleshooting pressure testing input and output lines with no leaks then the air is being introduced via the pump itself. This can be a motor shaft seal or the stainless endcap seal of the pump is allowing air into the system. Under pressure while testing a shaft seal pressure may hold but during dynamic use (spinning) it may be allowing air into the pump ahead of the impeller. You have done the correct troubleshooting you may be having a difficult time realizing the problem is the pump itself. When I have to troubleshoot a hard problem like this I make a re-circulation loop restricting the output line and use a liquid soap. If the re-circulated water bubbles after adding liquid soap water in suspect seal areas external to the pump, then the seals are failing. Food coloring water works too, but can discolor floors tiles or work areas.
Thanks for choosing FixYa,

Posted on May 12, 2011

thomas gowen

  • 92 Answers

SOURCE: Grundfos pump switches on & off continuously with

if you have a pump for the whole house you need to check the bladder tank. there is a air valve on the top. Check the pressure with a tire gauge you should have at least 20 PSI this will stop the pump from the on and off thing.

You can compress air yuo can not compress water. thats why the ballder tank. As the pump work to shut off pressure it is compressing air. then when you use a little water the pump does not run until a large about is run then the pump will re fill the system

Best of luck


Posted on Sep 08, 2011

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Grundfos pump

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Service support
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