With the water running the MQ pump runs intermittently

Bad regulator.

google Grundfos MQ3-45 check valve for more sites

copy and paste
https://rainwaterequipment.com/non-return-valve-for-grundfos-mq-3-45-or-mq-3-35-booster-pump/

https://www.pumpproducts.com/grundfos-96526663-non-return-valve-for-mq-booster-pumps.html



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Louise, since there is several different types and models of Grundfos pumps it would be hard to answer your question. To possible point you in the right direction below are a few links to where you can find some PDF documentation about a popular Grundfos pump the MQ series and direct link to the manufactures "Service Support".

Service support
Grundfos MQ Series Pumps

Sounds like the discharge is plugged. You can get the manual at: http://rainwatercollection.com/download/Grundfos-Manual.pdf

What type of pressure switch or pump controller on pump? Could be capacitor check. with power on try spinning fan at rear if starts probably cap. Have it checked. Could be controller faulty.

Pressure is bleeding back through the pump or system to the tank or well or where ever the water is coming from. Should be some sort of one way valve to keep water from going back to the source, mounted somewhere so that once pressure is pumped up, it will hold that pressure in the part of the system that has the pressure switch that controls the pump.

That or you have a leak where you can't see it. (Actually you do, it is just internal and not leaking outside the pipes!)

Hi Hayley.

Please allow me to try to help you.

Random water pumping or intermittent water pumping, appears to be quite a commonality with the Grundfos pump. The solution to this is quite a bit of process, the details of which you can get here...
http://inspectapedia.com/water/Intermittent-Water-Pump-Cycling.php

I have also attached a video, trust that gives you a bit more insight.

Hope that helps.

Best wishes. Regards.

This sounds like a issue with air still being in the system and not being removed from the system to make things work properly. I did try to findthere number and was unable to locate it. The only other option for you is to return the product and find one with better support

I have the same problem and have found that the inlet check valve has a broken shaft in the center of device. It is a multi-piece plastic unit and it looks as if it is not quite seating and therefore the internal pressure leaks slowly back into my low pressure suction line. The pump will start and the pressure will build then shut off for about 30 minutes then cycle again. I am going to replace the check valve.