serin labs

Troubleshooting

Solutions to common issues during flashing, setup, and operation.

Flashing & USB

Device not detected on USB / no serial port appears
  • Use a USB data cable, not a charge-only cable. Test the cable by transferring files to a phone or another device.
  • Install the SiLabs USB-to-UART drivers if your OS does not detect the device.
  • Try a different USB port — preferably directly on the computer, not through a hub.
  • Ensure you are using Chrome, Edge, or Brave. Web Serial is not supported in Safari or Firefox.
Flash fails or times out
  • Hold the BOOT button on the board while initiating the flash.
  • Try a shorter USB cable — long cables can cause communication issues.
  • Close any other serial monitors or programs that may be using the port.
  • Refresh the flash page and try again.
"Browser does not support Web Serial" message
  • Use a Chromium-based browser: Chrome, Edge, or Brave.
  • Safari and Firefox do not support Web Serial.
  • On Chrome, ensure the Web Serial API is enabled at chrome://flags/#enable-experimental-web-platform-features if needed.

WiFi & Connectivity

WiFi access point does not appear
  • Wait at least 60 seconds after powering on — the AP may take time to start on first boot.
  • Ensure the device is powered by a stable 5V source (at least 1A).
  • ESPHome: AP name is serin-XXXX (password: serinlabs).
  • HomeKit: AP name is Serin-XXXX (password: serinlabs).
  • If the device was previously configured, it may already be connected to your WiFi. Check your router's DHCP client list.
Device connected to WiFi but cannot find its IP address
  • Check your router's DHCP client list for a device named serin or similar.
  • Use a network scanner like Fing or nmap.
  • ESPHome: The ESPHome dashboard in Home Assistant shows the device IP automatically.
Device keeps disconnecting from WiFi
  • Check signal strength — the device may be too far from your access point, especially when installed inside the HVAC unit.
  • Use a 2.4 GHz network. ESP32 devices do not support 5 GHz WiFi.
  • Avoid DFS channels on your router, which can cause intermittent drops.
  • HomeKit: The fallback AP activates automatically after 5 minutes of disconnect.
Cannot access captive portal at 192.168.4.1
  • Disable mobile data on your phone — it may route traffic away from the AP.
  • Forget other WiFi networks temporarily to ensure your device stays connected to the setup AP.
  • ESPHome: Try http://192.168.4.1 manually in a browser.
  • HomeKit: Try http://192.168.4.1:8080.

ESPHome / Home Assistant

Device not showing as "Discovered" in ESPHome dashboard
  • Verify the device is connected to WiFi — check your router's DHCP client list for a device named serin.
  • Ensure the device and Home Assistant are on the same subnet/VLAN.
  • Check that mDNS is not blocked by your router or firewall. Some enterprise networks and certain UniFi configurations can block mDNS.
  • Try restarting the ESPHome add-on in Home Assistant (Settings → Add-ons → ESPHome → Restart).
  • As a fallback, add the device manually by IP address in the ESPHome dashboard.
Clicked "Adopt" but install fails or times out
  • Ensure the device is reachable on the network — try pinging its IP address.
  • Check that the ESPHome add-on has enough resources — the first compile can be memory-intensive.
  • If OTA fails, connect the device via USB and re-flash from the flash page, then re-adopt.
Climate entity shows as "unavailable" in Home Assistant
  • Check that the CN105 cable is firmly connected on both ends.
  • Verify the HVAC unit power is on — the device communicates via the unit's control board.
  • Check ESPHome logs for UART communication errors (visit the device IP in a browser or use the ESPHome dashboard logs).
  • Ensure TX/RX wires are not swapped — refer to the wiring reference.
OTA update fails in ESPHome
  • Ensure the device is reachable on the network — try pinging its IP.
  • Check available flash space — very large configurations may exceed memory.
  • As a fallback, connect via USB and use the flash page to re-flash.

HomeKit / Apple Home

Device not appearing in Apple Home for pairing
  • Ensure your iPhone/iPad is on the same WiFi network as the device.
  • Try scanning the QR code from the web UI at http://<device-ip>:8080.
  • If the device was previously paired, use Reset Pairing in the web UI first.
  • Restart the Home app and try again.
"Accessory Not Found" or pairing fails
  • Reset pairing from the web UI, then try adding the accessory again.
  • Ensure no firewall is blocking mDNS/Bonjour traffic on your network.
  • Reboot the device by unplugging and re-plugging power.
  • Force-close and reopen the Home app on your iPhone/iPad.
Web UI at port 8080 not loading
  • Confirm the device IP address in your router's DHCP list.
  • Use http:// (not https://) — the device does not support SSL.
  • If the device lost WiFi, it may be in AP mode — connect to the Serin-XXXX network and try http://192.168.4.1:8080.

HVAC / CN105 Connection

CN105 connected but no data / climate entity unavailable
  • Verify cable orientation — check the wiring reference for correct pin mapping.
  • Ensure the HVAC unit power is on at the breaker.
  • Confirm your unit has a CN105 port (not CN110). Check compatibility.
  • Check device logs for UART communication errors.
  • Try reseating the cable on both the CN105 and Grove connector ends.
Temperature readings are wrong or missing
  • Some units report 0°C until the compressor runs for the first time — this is normal.
  • For more accurate room temperature, use a remote temperature sensor from Home Assistant instead of the unit's built-in sensor.
  • Check that the unit is compatible and communicating (other climate controls should work).
Commands sent but HVAC does not respond
  • Check TX/RX wiring — they may be swapped. Refer to the wiring reference.
  • Verify the device is receiving 5V power from the CN105 port (a multimeter helps).
  • Some units need 30+ seconds after power-on before accepting serial commands.

Firmware & Recovery

How to factory reset the device
  • ESPHome: Re-flash via USB using the flash page. This resets all settings.
  • HomeKit: A 10-second long-press on the board button erases stored WiFi credentials. To fully reset, re-flash via USB.
How to switch between ESPHome and HomeKit firmware
  • Connect the device via USB-C to your computer.
  • Go to the flash page and select the other platform.
  • Flash the firmware — this completely overwrites the existing firmware.
  • WiFi credentials will need to be re-entered after switching.
OTA update fails or device appears bricked
  • USB flash always works as recovery. Connect via USB-C and use the flash page.
  • HomeKit: The firmware has automatic rollback — if validation fails after an OTA update, it reverts to the previous firmware.
  • If the device is unresponsive, hold the BOOT button while plugging in USB, then flash.

Still Need Help?

If your issue is not listed above:

When opening an issue, include your device logs, board type, and firmware version to help with diagnosis.

Disclaimer

This is an independent open-source project. It is not developed, endorsed, or certified by Apple Inc. or Mitsubishi Electric Corporation. Modifying HVAC systems may void warranties and carries risks. Proceed with care. This project is provided as-is, with no warranties or liability.