If you’ve been trying to add an ESP32/ESP8266 device to Home Assistant using ESPHome and ran into this frustrating message:
“An error occurred. Improv Wi-Fi Serial not detected”
…you’re definitely not alone! This error pops up right after flashing the firmware when ESPHome tries to configure Wi-Fi via the web serial interface and can stop you from getting your device connected to your network. Home Assistant Community
But after lots of trial and error, here’s a simple trick that worked for me — and might help you too.
🔍 What Causes the Error?
This message comes from the Improv Wi-Fi provisioning process — a method ESPHome uses to send Wi-Fi credentials to your device over serial after flashing. Some boards (especially certain ESP32 variants) don’t immediately exit flash mode after installation, so the web tool can’t detect the serial interface properly. Home Assistant Community
🛠 The Fix That Worked for Me
Instead of trying to configure Wi-Fi right away after flashing, do this:
- Flash the firmware normally using the ESPHome dashboard or web installer.
- When the installation completes — disconnect the device physically (USB cable).
- Reconnect it again to your computer.
- In the ESPHome dashboard (or web installer), click the three-dot menu next to the device.
- Choose Configure Wi-Fi from the menu and follow the prompts.
👉 This forces the device out of flash mode and ensures the browser can talk to its serial port reliably.
📌 Why This Works
Right after you flash a board via web serial, the device can stay in a special USB/flash mode that prevents serial detection for Improv Wi-Fi. Pulling power and reconnecting gets the chip into its normal run mode — so when you ask Home Assistant/ESPHome to “Configure Wi-Fi” from the menu, the serial connection is live and the credentials are sent correctly. Home Assistant Community
🧠 Bonus Tips & Troubleshooting
Here are a few additional insights from the community that might help:
📌 Board Types Matter
Some ESP32 variants (especially newer C3/S2/S3 chips) are more likely to trigger this error due to quirks in how they handle serial and Improv provisioning. GitHub
📌 Try Flashing Directly from the Home Assistant Server
If you continue to have issues, installing via USB directly from the Home Assistant host (rather than through your laptop) can sometimes avoid race conditions that lead to this error. Home Assistant Community
📌 Drivers & Serial Interfaces
If you’re using a USB-to-serial adapter (especially on Windows), ensure the correct CH340/CP210x drivers are installed — old or missing drivers sometimes break serial detection. Home Assistant Community
📌 Alternative Wi-Fi Setup
If the Improv method keeps failing, many boards will fall back to access point mode — where you connect to the device’s own Wi-Fi network and enter credentials manually. Home Assistant Community
🧩 Summary
If you hit “Improv Wi-Fi Serial not detected” after flashing an ESP device:
✅ Don’t panic — it’s common
✅ Flash normally and wait for success
✅ Physically disconnect & reconnect the board
✅ Then use the three-dot menu → Configure Wi-Fi
This workflow has helped many users get past the error and finish Wi-Fi setup successfully.
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