F3 fault - does this sound like bad CU200?

ElizabethElizabeth Registered Users Posts: 2

F3 fault on my Grundfos CU200 – outside Globe AZ. The well is 8 years old, 500’ deep, 2 GPM (less now) and set up with Grundfos 3 SQF-3 pump, CU200, IO 101, solar, plus grid power on a manual spring timer (use sometimes at night or cloudy days). No prior problems.

Odd thing: the fault occurred using the timer Saturday (cloudy). But over the days since, turning on the timer no longer results in fault indicators -  the box just stays unlit. However, when the solar panels come online it DOES display the fault indicators (such as when I reconnected them after closing up the boxes). However, “000” is displayed briefly and I thought I saw the rising arrows (for pumping), then it switches to fault light/F3. Also, once when I turned on grid power it did the same little dance, but not now – no display. BTW the “3” looks like an upside down “F” – top LED segment missing. I have also turned off and on the IO 101.

Opened the two boxes with my handyman and nothing obviously amiss. Cleaned out a few dead spiders – mostly in the IO 101.

Do the changing display suggest the CU200 going bad? (Shouldn't the F3/fault always be on with a pump problem?) Anyone in the Phoenix/Globe with expertise re: Grundfos SQFlex? How to get a “known good” CU200 without wasting $800 if it’s not the problem? Any advice?

Context: There is also a shared well (7 homes), but it went dry a month ago – local mine has diverted City waste outflow water from our canyon a few months ago. 8 years ago, pumping the rested well on grid power (fixed 2.5 GPM) the CU200 would start up at 320-330 watts. That was constant until last summer when the water was diverted. The last startup was at 360 watts, implying about a 60-foot ground water drop. It may drop further and kill the well, so I am on the fence about expensive repairs. We are about to drill down the shared well, fingers crossed.  I have 90 young fruit, nut and olive trees.



  • geosierranevadageosierranevada Registered Users Posts: 37 ✭✭✭
    Bypass the cu 200 and apply 110 volts to the pump and see if you get water. You can run a sqflex without the control box on AC or dc.
    Off grid for 18 years. 5KW panels, Trace sw4024, Bergy XL1 wind generator, GB forklift battery.  3 SQF 2 well pump, 12kw back up gen.  Not easy living in the wilderness but it keeps you busy
  • ElizabethElizabeth Registered Users Posts: 2
    Thank you George!

    If the pump produces water, then the pump and wiring are OK, and are we sure it's the CU200 that's bad? Looks like the grid power goes straight to the CU200, while the solar panels and pump go thru the IO 101. If the the IO 101 were at fault and the CU200 good, it would pump on grid power?
  • jnelmsjnelms Registered Users Posts: 1
    I am having the same code on my cu200 I sent it in for warrenty and received a new one and it still has the f3 code. The pump runs and pumps water when I test it in a water tub with 110 ac power hooked to it. I not sure if I should put it in the well (set at 735ft) I cant seem to find any tech support any place. Can anyone help.
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,910 ✭✭✭✭✭
    The CU electronics are susceptible to surges. They should have external SPD's on or off grid.
    Who did you buy this from? They are the support.
    You guy's need to state what you have done to test for anyone to help here.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • RangemanRangeman Registered Users Posts: 1
    I replaced my SQ3-2  on a Cu200 with an SQ6-2  and I get an F3 fault reading.  Any suggestions on what to do next?
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,910 ✭✭✭✭✭
    Need more info. Is it new, where did you buy cu-200, what is in the system? how is it wired? off-ongrid, did it ever work.........

    The answer you get will only be as good as the time you put into this.

     Been using this combo, dozens of times, along time, without issues other than lightning and normal wear and tear..
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • Wyandotte82Wyandotte82 Registered Users Posts: 9 ✭✭
    According to the manual page 9 an F3 means " no contact to the pump ".
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