My Grundfos MQ pump won't start after it has been idle for 4 to 5 weeks. It is installed at my weekend place in the country. This has happened several times. Pump was replaced once but problem continues.

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

Is it newly installed or has it been working for a while till you noticed it?

Check the capacitor or the centrifugal switch.

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!)

Does your system equipped with pressure tank (pneumatic tank)? If it has, maybe it's already filled with water due to some pinhole leaks. Drain the tank and see what will happen.

Sounds like it may be air in the system - there is a black plastic bleeder screw on the top of the pump - open it and let air escape, if any, then fill with water, close screw and start pump.

This is a problem with your bladder in the pressure tank or the pressure switch. Ether one will produce this cycling on and off. Good luck.