Conext SW Fault Code F57 F58 - FET1 Over Temperature

prgrod01prgrod01 Registered Users, Users Awaiting Email Confirmation Posts: 3
I have a small cabin utilizing a 100% off grid solar/generator/inverter setup. It has been working well for many years but recently ran into a problem with a fault code on our Schneider Conext SW inverter. 

The F58 FET1 Over Temperature fault code is preventing the inverter from operating. The fault is intermittent and does reset, but will come back sometimes in minutes, sometimes in hours, and has comes on immediately upon system startup when the inverter is cold. ambient temperature is 4-6 deg C at our last outing. 

If the inverter FET's are running hot, this might imply a heavy load and the inverter running hot, but were running  a few LED lights and still had a problem. Has anyone come across this fault and/or resolved the issue?

Thanks in advance.


  • RCinFLARCinFLA Solar Expert Posts: 1,460 ✭✭✭✭
    If heat sink is not getting hot, it sounds like a bad temp thermistor or bad thermistor connection.  Check if there is control panel setup view that shows FET temp reading.  Check if temp is off actual temp or jumps around indicating possible intermittent connection.

    They typically use 10k thermistor although there are several different temp coefficient profiles.
  • prgrod01prgrod01 Registered Users, Users Awaiting Email Confirmation Posts: 3
    edited April 21 #3
    Got it all taken apart, a few dozen screws later and it was pretty straight forward to troubleshoot. The FET2 thermistor value was ,<3k ohms and FET1 thermistor value was around 39k ohms. The thermistor is glued to the far end FET with green epoxy. 

  • PhotowhitPhotowhit Solar Expert Posts: 5,824 ✭✭✭✭✭
    I had a fan fail on my Prosine 1800, It would appear intermittent as it would work until it was producing over 400 watts then overheat. 

    The replacement was easy with a similar computer fan. Lasted 6 years in daily use until I replaced the inverter.

    Prosine fan replacement, Would you...? — northernarizona-windandsun (

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • prgrod01prgrod01 Registered Users, Users Awaiting Email Confirmation Posts: 3
    Just to close this out, I got both thermistors changed out at my local PCB repair shop and all is working as it should again... thanks for the help.
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