Grundfos CU200 - Always on

patbobpatbob Registered Users Posts: 1
edited March 2017 in Construction #1
I have a solar setup with a generator backup. CU200 SQFlex with a IO 101 SQFlex Switchbox. 

I recently found the tank overflowing. The CU200 is showing a full tank, is indicating water flow and the power switch is ON. The power switch is unresponsive. It will not shut off. To stop the water pumping I have to shut off the IO 101.

I've checked all the connections. Disconnected the Float Switch. No changes. My take is that the circuit board is fried and I need to buy a new controller.

Does anyone have any suggestions? I'm at a bit of a loss here.

Thanks in advance.


  • BB.BB. Super Moderators, Administrators Posts: 32,814 admin
    I don't have any knowledge about the product--But it sounds like the CU200 is bad.

    I suggest you call the installer (if not you) or Grundfos support.

    Otherwise, check wiring connections / screws / dirty connections--But probably a long shot.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,230 ✭✭✭✭✭
    Maybe it was hit with lightning! They are very reliable if they are protected and installed correctly. They will detect and record over voltage for warranty.
    "we go where power lines don't" Sierra Nevada mountain area
    E-mail [email protected]

  • Robert_WRobert_W Registered Users Posts: 14 ✭✭
    edited August 8 #4
    Recently found this searching for another issue with my CU200. Long answer short in case anyone else comes upon this. Mine has the same issue. Will not shut off even though tank is full. 

    Some where here a Grundfos rep responded that it was an issue with the first generation of CU200 controllers. The newer units have fixed the issue. Something to do with communication between the controller and pump at low power levels. Shutting off the breaker to reset was needed on older units. Including mine.

    As of 8/22 I am still using a CU200 from 2011. I have just learned to shut off power at the end of the day. 

    See this post.
  • JRHillJRHill Registered Users Posts: 115 ✭✭
    Originally I triggered my CU200 on and off with a standard well pressure switch to fill the system pressure tanks. I began to have the pump not shut down and the over pressure valve would pop off. I jacked and jacked with the system until I just bypassed the CU200 and used the well tank pressure switch for power to the pump. The CU200 is a pretty fancy box with the LEDs and the display but is NOT needed for the well pump. It works fine with just a standard pressure switch, I also have the IO101 for AC operation and it is just fine without the CU200. I disconnected the CU200 8 years ago and the system hasn't missed a beat.
    Two systems: 1) 2925w panels, OB VFXR3648, FM80, FNDC, Mate3s, 240 xformer, four SimpliPHI 3.8; 2) 780w, Morningstar 30a, Grundfos switch, controller and AC/DC pump, 8 T105. Honda EU7000is w/AGS. Champion 3100. Miller Bobcat.
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