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Program Not Running

BBC Micro:bit

Severity:

Source: OnlyErrorCodes.com — Every error code. One place.

Micro:bit Program Not Running — How to Fix It

What Does This Error Mean?

Micro:bit program not running after upload is usually caused by copying the .hex file incorrectly — the file must be dragged onto the MICROBIT drive, not into a subfolder. Also check that the yellow LED on the back stopped flashing (flashing = still programming).

Affected Models

  • Micro:bit V1
  • Micro:bit V2
  • Micro:bit V2.21

Common Causes

  • HEX file copied into a subfolder instead of the root of the MICROBIT drive
  • Copy interrupted before the flash process completed
  • Uploading a V2 .hex file to a V1 board or vice versa — wrong hardware target
  • Program runs but produces no visible output — LED matrix shows nothing by design
  • Micro:bit reset button pressed during programming interrupted the flash

How to Fix It

  1. Drag the .hex file to the root of the MICROBIT drive.

    Open File Explorer (Windows) or Finder (Mac) and locate the MICROBIT drive. Drag the downloaded .hex file directly onto the drive — not into any subfolder. Wait for the orange LED on the back of the Micro:bit to stop flashing, then the program will start automatically.

  2. Wait for the programming LED to stop flashing.

    The small LED on the back of the Micro:bit flashes orange during programming. Do not unplug or reset the Micro:bit while this LED is flashing. Programming typically takes 5–15 seconds. The program starts as soon as the flashing stops.

  3. Verify the HEX file matches the Micro:bit hardware version.

    MakeCode .hex files compiled for V2 will not run on a V1 board. In MakeCode, check the project settings and confirm the target hardware matches your physical Micro:bit. The hardware version (V1 or V2) is printed on the back of the Micro:bit board.

  4. Add visible output to your program.

    If your program runs but produces no visible output, it may appear as if it is not working. Temporarily add a 'show string Hello' block at the start so you can confirm the program launched. If 'Hello' appears, the program is running — the issue is in the program logic, not the upload.

  5. Press the reset button after copying.

    If the program does not start after the LED stops flashing, press the small reset button on the back of the Micro:bit. This forces a reboot and runs the newly flashed program from the beginning.

When to Call a Professional

If the Micro:bit shows a continuous red LED error pattern after every flash attempt, the flash storage may be corrupted. Try the MAINTENANCE firmware recovery procedure from microbit.org.