How I Fixed “Improv Wi-Fi Serial Not Detected” When Adding a New ESPHome Device in Home Assistant

If you’re flashing an ESP32 or ESP8266 with ESPHome and get this message:

An error occurred. Improv Wi-Fi Serial not detected

…it usually happens right after the firmware has been installed, when ESPHome tries to send the Wi-Fi details to the device over USB/serial.

I ran into this while setting up a board, and the fix ended up being surprisingly simple.

What worked for me

Flash the device as normal through ESPHome.

Once the install finishes, unplug the USB cable from the device completely.

Then plug it back in.

After that, go back to ESPHome, click the three dots next to the device, and choose:

Configure Wi-Fi

Follow the prompts from there.

That was enough to get the board detected properly and let ESPHome send the Wi-Fi credentials.

Why this seems to happen

After flashing, some ESP boards do not properly restart into normal running mode. They can stay in a weird flash/USB state, so the browser or ESPHome tool cannot see the serial connection properly for Improv Wi-Fi setup.

Unplugging and reconnecting the board forces it to reboot cleanly. Once it starts normally, the Configure Wi-Fi option can talk to the device correctly.

Things to try if it still fails

Some ESP32 variants, especially C3, S2, and S3 boards, can be a bit more fussy with serial provisioning.

A few things worth checking:

Make sure the USB cable is a proper data cable, not charge-only.

Try a different USB port.

On Windows, check that the correct USB-to-serial drivers are installed, such as CH340 or CP210x depending on the board.

Try flashing directly from the Home Assistant machine if you are currently flashing from another computer.

Some boards may also fall back to their own temporary Wi-Fi access point, which lets you connect to the device and enter your Wi-Fi details manually.

Quick version

When you see:

Improv Wi-Fi Serial not detected

try this:

1. Flash the ESPHome firmware.
2. Wait for the install to finish.
3. Unplug the board from USB.
4. Plug it back in.
5. In ESPHome, use three dots → Configure Wi-Fi.

That simple unplug/replug step is often all it needs.