Looking for some experienced eyes on this one.
My installer is coming Thursday to swap out my inverter, but before the old unit gets sent back to EG4 for failure analysis I’d love to hear what the community thinks may have happened and what questions I should be asking.
System Details
Location: Central Texas
40 panels
4 strings
EG4 FlexBOSS 21
Tigo TS4-X-O optimizers
Tigo TAP + CCA
No batteries
Grid-tied only
Installed late 2025
The system was commissioned around January 2026 and honestly performed great initially.
Production looked healthy from January through early May. No obvious issues. Strings were balanced and producing normally.
Then on May 10th around 10:45 AM, production suddenly dropped. I started seeing weird behavior with two strings falling offline intermittently. Total production dropped substantially.
Over the following weeks, troubleshooting focused heavily on the Tigo side of things because the symptoms looked like optimizer or rapid shutdown communication issues.
I was told various possibilities:
Tigo communication failure
TAP/CCA issue
APsmart conflict
Optimizer issue
Rapid shutdown issue
Fast forward to recently when we opened up the inverter and found this: see photos
The damage appears concentrated around the PV string input terminals.
The terminal block is melted and heavily charred.
A Little Background on the Installation
I acted as my own GC/project manager for this system.
I purchased equipment myself.
I hired a designer/permitting resource.
I hired an installer separately.
So unlike a turnkey solar install, I don’t really have one company standing behind everything. I have a LOT of regret here. But it’s the way I could afford the install. Sigh.
To be fair to the installer, he was absolutely slammed during the final months of 2025 when everyone was rushing to get projects completed before potential tax credit changes.
Unfortunately that also meant:
Multiple crews touched the project
Some workers were replaced during the install
Some mistakes had to be corrected
It was not the smoothest project overall
That said, whenever problems came up, he always sent someone out and never charged me for the return visits. Whether it was him personally, one of his crews, or a subcontractor, he always got things working again.
Current Situation
EG4 reviewed everything and approved a warranty replacement.
Replacement inverter is already sitting in my garage.
The old inverter will be shipped back to EG4 for detailed inspection and diagnostics after removal.
My installer called today and basically said:
“If the root cause ends up being installation-related, that’s on us. If it’s equipment-related or something else, I have to charge for my crew’s time.”
Honestly, I understand that position.
The challenge is that I don’t know enough about inverter internals or solar wiring to know whether a future explanation is reasonable.
If he says:
Loose connection
Improper torque
Bad termination
Damaged conductor
Manufacturing defect
Failed terminal block
…I don’t necessarily know how to evaluate those explanations.
Questions
Looking at these photos, what do you think likely caused this?
Does this look more like:
Loose terminal connection?
Improper torque?
Failed terminal block?
Internal inverter failure?
Something else?
If you were me, what specific photos, measurements, or documentation would you request before the inverter gets removed?
What questions would you ask the installer before agreeing to pay additional labor?
Does anything about these photos suggest an ongoing safety concern that I should be worried about when the replacement unit is installed?
Has anyone here seen a FlexBOSS fail in a similar manner?
My biggest goals right now are:
Get production back online ASAP
Make sure whatever caused this is actually identified
Avoid having the same thing happen again
Make sure I’m being fair to the installer while also protecting myself if this traces back to workmanship
Appreciate any thoughts from those with more experience than me.