One I-9PSL-DE refusing to connect to some UniFi APs, while another can

Nainokami · January 22, 2026, 9:21am

I have 3 airgradient monitors (2 x I-9PSL-DE and 1 x O-1PST) which have all worked without issue for well over a year, but recently one of my I-9PSL-DE is refusing to connect to some of my UniFi APs, more specifically it connects to U6-Pro and U6-Mesh (Wired), but refuses to connect to my 2 x U7-Pro XG and U7-Pro XGS.
The other I-9PSL-DE is connected and working fine to the U7 APs. The I-9PSL-DE in question is sitting very close to the U7-Pro XGS, but chooses to connect to the Garage U6-Pro instead. If I try to lock the I-9PSL-DE to the U7-Pro XGS it refuses to connect entirely.
It might be related to recent firmware updates on the U7 APs, but as the problem isn’t universal to all my AirGradient monitors it is a bit odd.

Bonus info: the I-9PSL-DE that works is the preassembled version, whereas the non-working is a DIY kit. But AFAIK they use the same ESP32C3, and it is soldered to the board, so I had nothing to do with the installation.
Is there any way to entirely reflash the I-9PSL-DE to see if that would help?

Tai_AirGradient · January 22, 2026, 10:42am

Hi @Nainokami , you can follow this video guide (if you prefer video) to entirely reflash your I-9PSL-DE: https://www.youtube.com/watch?v=L6oY8jS-1Do

Here is the link to the firmware page: AirGradient ONE (I-9PSL), Open Air (O-1PST) and Open Air Max (O-M-1PPST...) Firmware Versions

Please also check the ‘Erase device’ box:

Also, please be informed that the firmware on our firmware flashing tool is 3.3.8, but the latest firmware version available on the AirGradient dashboard is currently 3.6.0 (newer than what you can flash using our web firmware flash tool)

So, after you reflashed your I-9PSL-DE, successfully connected to your Wi-Fi, and established a connection to the AirGradient server, your I-9PSL-DE will detect that there’s a newer firmware and perform an OTA firmware update which would take some time.