Reply to Denky D4 - unable to reset on Wed, 01 Jul 2026 09:55:56 GMT

Charles — Wed, 01 Jul 2026 09:55:56 GMT

@ellipsis , yes you can try to press IO0 button (leave pressed) then press and release reset button (while leaving IO0 button pressed) then device should be in bootloader mode and readyr to flash as said @arnaud-r

Reply to Denky D4 - unable to reset on Mon, 29 Jun 2026 11:55:23 GMT

Arnaud R — Mon, 29 Jun 2026 11:55:23 GMT

@ellipsis

Hi,

This 'Sync timeout' error means the ESP chip is refusing to enter 'bootloader mode' (the mode needed to flash the firmware).

Here are the best ways to fix it:

Force Bootloader mode manually

If your Denky D4 has a BOOT button: Press and hold it.

While holding the BOOT button, press the Reset button once (or plug the USB cable in).

Release the BOOT button after 1 or 2 seconds.

Try the Web Flasher again.

(Note: If you don't have a BOOT button, you have to use a small wire to connect the GPIO0 pin to GND while plugging the USB in).

Use a better flashing tool
Web browsers sometimes struggle with the ESP timing. Instead of the Web Flasher, download a standalone software called ESP-Flasher. It is usually much more reliable.
Check your hardware

Make sure you are using a high-quality USB data cable (some cables only provide power).

Plug the USB cable directly into your computer's motherboard, avoiding USB hubs or extension cords.