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Thread: Pump Stops and Starts

  1. #1
    DIY Junior Member bwasow's Avatar
    Join Date
    Jan 2012
    DC and Mexico

    Default Pump Stops and Starts

    Our home water system in Mexico works like this:
    City water is delivered a couple of hours a day to our cistern.
    From the cistern, it is pumped every few days to a 1100 liter tank on the roof.
    From the rooftop tank, the water enters a Grundfos MQ-35 pressure booster pump.
    Leaving the pump, the water passes through two filters, one for sediment and one with activated charcoal.
    Finally, the water passes through a unit that uses electric sparks to soften it (changing carbonates to bicarbonates, or something like that) and kill most germs.
    Then it enters our two story house.

    My problem is that when water is running continuously in the house, the Grundfos pump cycles on and off every ten seconds or so. I fear it will wear out. I think this is a new problem; I did not notice it before. The pump has perhaps 18 months of daily use on it.

    I thought that the filters might be clogged, backing up pressure to the pump. Rinsing the filters did not help. Also, the flow in the house is good (although water pressure cycles with the pump).

    Can anyone offer me advice? By the way, this is a small town with a limited range of plumbing expertise.


  2. #2
    In the Trades Tom Sawyer's Avatar
    Join Date
    Nov 2010


    Find the manual that came with the pump or download if online. Run the system check an make sure the pump is properly adjusted. I suspect the cut in / cut out settings are not correct or...............the pump is defective.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  3. #3
    Moderator valveman's Avatar
    Join Date
    Mar 2006
    Lubbock, Texas


    You would be much better off with a standard jet pump, small pressure tank, and a pressure switch. I am pretty sure it is going to be the electronics in the pump that are bad. That MQ is made to sell. They don't last very long. The trash bin is where I find most of those Grundfos MQ pumps.

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