Grundfos Garden - Recent Questions, Troubleshooting & Support

The bearings fitted to this pump are lubricated for life - if the noise is bearing related they will need to be replaced. If the noise is not from the bearings you will need to establish the cause - possibilities are:
Cavitation (sounds like frozen peas inside the pump!) caused by restricted suction - check for blocked strainer etc.
Foreign matter in the pump....
Loose impellers
Sometimes a piece of wood or a large screwdriver used as a stethoscope can be very handy in determining where abouts in the pump the noise is coming from.
Given more specific information I can suggest the next course of action.
Good luck
Mike G

Grundfos MQ3-35 ... | Answered on Jun 29, 2019


Grundfos Garden | Answered on Mar 28, 2019

three phase
three phase power = 1.5Kw
single phase = 1.5KW/3
kw = 500w/.86 (.86 is power factor)
kva = 581.39 watts
current = kva / voltage
voltage = ? 120 v at guess
current = 581.39 / 120
current one phase = 4.84 amp
three phase = 4.84 x 3
14.53 amps
240v would come out as 7.26 amps

Grundfos Garden | Answered on May 03, 2018

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.

Grundfos MQ3-35 ... | Answered on Oct 02, 2017

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.

Grundfos MQ3-35 ... | Answered on Oct 02, 2017

If you can not hold your hand on the motor for a count of 10 when it has cut out, the motor has overheated and needs to be replaced or find some reason for an overload.

Grundfos Garden | Answered on Jun 21, 2017

Pump probably runs dry, try to fill up the pump with water a few times and see what it gives. If the pump heats up then the rotor is turning but no water moves, pressure is not building up. Pressure switch is maybe faulty. If you have the possibility to connect a pressure gauge after the dicharge you can see if the pressure is building up or not.

Grundfos MQ3-35 ... | Answered on May 25, 2017

Check the capacitor or the centrifugal switch.

Grundfos MQ3-35 ... | Answered on May 01, 2017

something wrong here. your incoming pressure is 4 psi ( tank pressure to the pump and you use a pump to boost pressure to a maximum of 65 psi at which point the pump is shut off ( all taps close off)
yet with no pumps running the pressure goes up to 100 psi
Find where you are getting pressure in that is making the pump leak
if you have 100 psi to the pump when it is turned off, then it would not be turning on ( power on) as the shut off pressure is set at 65 psi and the line pressure is 100 psi

Grundfos MQ3-45 ... | Answered on Sep 27, 2016

Over revving is normally caused by air in the pump, or that the impeller has broken off. In you case I think it is the latter and the broken impeller is jamming the motor and that is what is causing the hum. The only thing to do is remove it and strip it down.

I used to live in Leighton Buzzard where the head office is, and have a friend who works for them.

Grundfos Garden | Answered on Apr 01, 2016

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