FRITZ!Box 4020 Service - Knowledge Base

FRITZ!Box 4020 Service

"Info" LED flashes red or several LEDs flash constantly

The "Info" LED flashes red or several LEDs flash continuously and the FRITZ!Box freezes.

In this case

  • you may no longer be able to open the FRITZ!Box user interface (
  • only a white page with the error message "firmwarecfg: ERROR Error: opening page ../html/index.html" may be displayed in your web browser.


  • A manual or automatic FRITZ!OS update failed.

Simply proceed as described below. After each measure, check whether the issue persists.

1 Preparations

The following preparations are necessary for the measures below. They always must be carried out:

Restarting the FRITZ!Box

  1. Unplug the FRITZ!Box.
  2. Plug the FRITZ!Box back in after about 5 seconds.

    Note:The FRITZ!Box settings remain intact. The restart will take about 2 minutes. During this time, you cannot access the FRITZ!Box.

Clearing the cache of your web browser

Clear the cache of your web browser:

  • Google Chrome
    1. Click the button (Customize and control Google Chrome) on the top right of Chrome.
    2. Click "More tools" and then "Clear browsing data...".
    3. Select "the beginning of time" in the "Clear browsing data" window.
    4. Select "Cookies and other site and plugin data" and "Cached images and files".
    5. Click "Clear browsing data".
  • Mozilla Firefox
    1. Click the (Open menu) button on the top right of Firefox.
    2. Click "Library" and then "History".
    3. In the history, click "Clear Recent History".
    4. Select "Everything" and click "Clear Now".
  • Microsoft Edge
    1. Click the button (More actions) in the top right corner of Edge and then click "Settings".
    2. Click "Choose what to clear" under "Clear browsing data".
    3. Enable the option "Cached data and files" and click "Clear".
  • Microsoft Internet Explorer
    1. Click the button (Tools) on the top right of the Internet Explorer.
    2. Click "Internet Options" and then "General".
    3. Click the "Delete" button.
    4. Enable the option "Temporary Internet files" and click "Delete".
  • Apple Safari
    1. Click "Safari" in Safari's menu bar and then click "Preferences".
    2. Click "Advanced" in the settings and enable the option "Show 'Develop' menu in menu bar".
    3. Click "Develop" in the menu bar and then click "Empty Caches".
    4. Click "Safari" in the menu bar and then click "Reset Safari".
    5. Click the "Reset" button in the next window.

2 Checking whether the update was successful

  1. Open the FRITZ!Box user interface.
    • If the user interface still does not open several minutes after the "Info" LED has gone out:
      • Use the recovery tool to reset the FRITZ!Box. The recovery tool then installs the update.
  2. Check which FRITZ!OS version is displayed on the "Overview" page.
    • If version 6.83 is displayed, then the update was successful.
    • If an older version is displayed:
      • Repeat the online update procedure.
        • If the online update fails, perform a manual update as described in the next section.

3 Repeating the update process

Downloading the FRITZ!OS file again

The FRITZ!OS file may not be suitable for your FRITZ!Box, or the file may not have been downloaded completely. Therefore, download the file again:

  1. Call up in your web browser.
  2. Switch to the folder for your FRITZ!Box model, then to the subfolder "firmware", and then to the folder named "deutsch" or "english".

    Note:The complete model name of your FRITZ!Box is displayed in the FRITZ!Box user interface on the "Overview" page and on the underside of the device.

  3. Download the latest FRITZ!OS version for your FRITZ!Box with the file extension ".image" to the computer.

Clearing internet connection and closing all active programs

  1. Remove the cable connecting your FRITZ!Box to your DSL line or the device establishing the internet connection.
  2. Close all active programs running in the background on your computer such as virus scanners, firewalls, etc.

    ATTENTION!Only disable firewalls when updating FRITZ!OS and re-enable them before establishing an internet connection. This software protects your computer from attacks from the Internet and prevents other threats (for example computer viruses) from being executed.

Connecting the FRITZ!Box with the computer

  1. Use the network cable included with delivery to connect the computer directly to a "LAN" port on the FRITZ!Box. 
  2. Clear all other connections between your FRITZ!Box and network devices or USB devices.

Updating manually

  1. Click "System" in the FRITZ!Box user interface.
  2. Click "Update" in the "System" menu.
  3. Click on the "FRITZ!OS file" tab. If the tab is not displayed, enable the Advanced View first.
  4. Click "Save Settings".

    Note:Save your FRITZ!Box settings again under "System > Backup" right after successfully completing the installation. Then you can always restore it to a working configuration.

  5. Click the "Browse..." button.
  6. Select the FRITZ!OS file that you downloaded (image file) and click the "Open" button.
  7. Click the "Start Update" button.

4 Resetting the FRITZ!Box

If you also cannot perform a manual update, use the recovery tool to install the latest FRITZ!OS:

Saving the FRITZ!Box settings

Applying the recovery tool

Restoring the FRITZ!Box settings