How to fix
0x800f0821 error when installing optional features
on Windows

On Windows, I received error code 0x800f0821 when trying to install optional features via settings. I have no clue why this is happening - everything else seems to work fine.

0x800f0821 is a common error that arises whenever users attempt to install optional Windows features - utilities such as .NET Framework, language packs, graphics utility, or some other system items that assist in enhances Windows functionality. Instead of the installation process proceeding, it fails and gives the 0x800f0821 error, making it not possible for users to add the required feature.

The 0x800f0821 can arise from multiple sources, as detailed below, with user experiences highlighting the frustration of repeated failures:

• Corrupted system files
• Windows Update dependency failures
• Network issues
• Conflicting system settings or damaged update components

Users commonly report that repeated installation attempts, even with administrator privileges, consistently fail. This issue can be particularly disruptive, as many of these features are essential for specific operational requirements. Furthermore, some instances of this error have been observed following recent Windows updates, indicating that system modifications may contribute to its occurrence.

To resolve the 0x800f0821 error, users may be required to check for component corruption in Windows, reset update services, or manually install the feature using alternative options. If the issue persists, automated software utilities can be extremely helpful in resolving more complicated system issues.

The [d1] repair and maintenance tool is an efficient and handy means of identifying and resolving Windows component-related issues so optional features may be installed without interruption in the future.

Fix 1. Use the Windows features menu instead of settings

Sometimes, installing optional features through the Windows Features menu works when the Settings app fails.

• Type optionalfeatures in Windows search and press Enter.
• Locate the optional feature you want to install and check the box next to it.
• Click OK and let Windows apply the changes.
• Restart your computer and check if the installation was successful.

Fix 2. Run the Windows Update and Network troubleshooters

Since many optional features rely on Windows Update, running the troubleshooter can help detect and fix any related issues.

• Type Troubleshoot in Windows search and hit Enter.
• Select Additional troubleshooters/Other troubleshooters.
• Find Windows Update from the list and select Run the troubleshooter/Run.
• Wait till the scan is finished - you will be provided with potential causes so you can proceed with fixes.
• Repeat this process with Network troubleshooter.

In Windows 10:

• Right-click on Start and pick Settings.
• Go to the Network & Internet section.
• On the right side, find the Advanced network settings section.
• Click Network troubleshooter and wait.
• The fixes will be automatically applied.

Fix 3. Reset Windows update components

Corrupt Windows Update files or services can prevent optional features from installing properly. Resetting update components can fix this.

• Type cmd in Windows search.
• Right-click on Command Prompt and pick Run as administrator.
• User Account Control window will show up - click Yes when prompted.
• Paste in each of these commands, pressing Enter every time:
  net stop bits
  net stop wuauserv
  net stop appidsvc
  net stop cryptsvc
  Del “%ALLUSERSPROFILE%\Application Data\Microsoft\Network\Downloader\*.*”
  rmdir %systemroot%\SoftwareDistribution /S /Q
  rmdir %systemroot%\system32\catroot2 /S /Q
  regsvr32.exe /s atl.dll
  regsvr32.exe /s urlmon.dll
  regsvr32.exe /s mshtml.dll
  netsh winsock reset
  netsh winsock reset proxy
  net start bits
  net start wuauserv
  net start appidsvc
  net start cryptsvc 
• Reboot your system.

Fix 4. Manually install the optional feature

If Windows fails to download the necessary files automatically, you can manually install the feature using DISM (Deployment Image Servicing and Management).

• Open Command Prompt as Administrator.
• Type the following command and press Enter to view available optional features:
  dism /online /get-capabilities
• Identify the feature you want to install, then type:
  dism /online /add-capability /capabilityname:<FeatureName>
  Replace <FeatureName> with the actual name of the feature from the list.
  Wait for the installation to complete, then restart your computer.

Fix 5. Run SFC and DISM scans

Corrupted system files can interfere with feature installation, causing the 0x800f0821 error. Running system scans can repair missing or damaged components.

• Open Command Prompt as Administrator.
• Use the set of the following commands, pressing Enter each time:
  DISM /Online /Cleanup-Image /CheckHealth
  DISM /Online /Cleanup-Image /ScanHealth
  DISM /Online /Cleanup-Image /RestoreHealth
  
• (Note: if you get an error executing this last command, add /Source:C:\RepairSource\Windows /LimitAccess to it and try again).
• Close down the Command Prompt and restart your computer.
• After DISM completes, run sfc /scannow again to check if the issue is resolved.

Fix 6. Enable Windows Modules Installer service

This service is required for installing and managing Windows components. If disabled, the 0x800f0821 error may appear.

• Type Services in Windows search and hit Enter.
• Scroll down to find Windows Module Installer service from the list.
• Double-click to open Properties.
• Under the Startup type, select Automatic from the drop-down menu.
• Click Start and OK.

Fix 7. Install the feature using an ISO file

If all else fails, manually installing the feature from a Windows ISO file can bypass update-related issues.

• Download the latest Windows 10 ISO from the official Microsoft website (Windows 11 version).
• Mount the ISO by right-clicking it and selecting Mount.
• Open Command Prompt as Administrator and use the following command:
  dism /online /add-package /packagepath:D:\sources\sxs\<FeatureFile>.cab
• Replace D: with the mounted drive letter and <FeatureFile> with the correct package name.
• Restart your computer and verify if the feature is installed.