Fronius IG 4000 power output reduced by 1/3


New Member
We just went through a reinstallation process and, well, it's an interesting story.

We removed and reinstalled the panels (the pro installers 15 years ago used the wrong mounts and the roof was leaking badly - that's another story). In the process, we discovered 2 places where the panel wires may have shorted to ground and fixed those. The new installation has the correct mounts and fully-grounded rails and clamps. And when we turned the IG 4000 back on, we got over 3kW which matched the specs. Happy day!

And it ran to peak 3kW+ for 2 days (I have an Emporia Vue power monitor connected to the smart meter that generates data logs that I'm looking at - the house was unoccupied so there's very little load).

But the next day I came to the house, the inverter was stuck in Startup and I can't recall the error codes (might have been a 101 or 107) - Zero kW. So at that point (that was late August) I thought the inverter was toast and I was going to have to call in a service person to sort it out.

Then the next day, I go to the house and flip the inverter on just for jollys, and the darn thing boots fine, no error codes, no 516, but there's a difference - it maxes out at 2kW. And it's been running the same ever since - no error codes but 1/3 less max power on a sunny Santa Cruz day.

The configuration is 3 strings of 9 x 175W Kyoceras so I'm thinking we've lost a string due to a loose connection (we were super careful when we put the panels back - there were 2 of us checking each others work). But my wife and I tested that hypothesis today and it looks like we're getting power from all 3 strings - when we covered each string, the power dipped appropriately. And no error codes.

There was a time before we did the panel removal and reinstall when the inverter was working but was sometimes making a lot of buzzing and clicking when the sun was right overhead but no error codes. I don't know whether this inverter has stages and we've lost an output stage or what - but we're definitely at a ceiling of around 2050W since we hit 3218W the day we turned it back on after the reinstall.

So to recap... we reinstalled the panels, saw about 3.2kW max for a couple of days, then the inverter went down with some error codes for a day (and I shut it down completely isolated), and then the next day the inverter came up again but now the max is about 2.05kW (like I got an IG 2000) and its been that way ever since for over a month now.

Anyone have any ideas?

Thanks, Joe


Solar Addict
Inverter will de-rate output power, generally for over-temperature. It may not throw an error code.
Do you hear cooling fans running?

Fronius has good 5-year warranty.

Was the inverter started properly? DC first then AC


New Member
The problem occurs all the time - from startup to hours later so it's not cooling related - it's consistently down 1/3. A tech told me that there are two power stages in the IG 4000 so it's possible the second stage has a fault and he showed me how to check the code for the second stage. Or something like that.

The unit is out of warranty - we've had it replaced twice, the last time was 7-10 years ago.


New Member
It's always 1/3 lower regardless of operating temperature, whether I hear fans or no fans.

If I recall correctly there is separate error code reporting for PS0 and PS1 on an IG 4000 - PS1 being the second power stage. He said that the first power stage handles up to 2000 watts and then the second power stage kicks in. Sounds like my second power stage is shot. Just curious whether anyone else with a Fronius has seen this, and, if so, what part needed to be replaced?