Cannot install Windows 11 25H2

Robert ONeill 60 Reputation points
2026-10-01T17:22:04.53+00:00

Error message: We couldn't update the system reserved partition

Windows for home | Windows 11 | Windows update
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  1. AI answer

    2026-10-01T17:22:19.41+00:00

    This usually means Windows Update cannot write to the System Reserved partition or EFI System Partition because there is not enough free space there.

    For Windows 11 25H2, start with these steps:

    1. Install the latest available update first.
      A known Windows 11, version 25H2 issue where updates failed with 0x800f0922 because of low free space on the EFI System Partition was resolved in updates released May 26, 2026 (KB5089573) and later.
    2. If the device is still on an update released before that date and the install keeps failing, use the documented workaround below.
    3. Workaround: set the ESP padding registry value to allow the update to install.
      Warning: Editing the registry incorrectly can cause system issues. Back up the registry first.
      • Open Command Prompt as Administrator.
      • Run: 
             reg add "HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc" /v EspPaddingPercent /t REG_DWORD /d 0 /f
      • Restart the PC.
      • Try Windows Update again.
    4. If the device is a consumer or non-managed PC, restart once or twice and retry.
      Microsoft states this issue is also mitigated through Known Issue Rollback (KIR), and the fix propagates automatically to consumer and non-managed business devices.
    5. Also check the common causes for 0x800f0922:
      • Disconnect any VPN before retrying Windows Update.
      • The error can also indicate insufficient free space in the System Reserved partition.
    6. Before retrying the upgrade, apply the standard upgrade fixes:
      • Unplug nonessential external hardware.
      • Install all important Windows updates.
      • Temporarily uninstall non-Microsoft antivirus software.
      • Uninstall nonessential older software.

    If the failure message remains generic, check the exact code in Start > Settings > Windows Update > Update history and use that code for the next troubleshooting step.

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  2. Ramesh 182K Reputation points Volunteer Moderator
    2026-10-01T17:45:10.0366667+00:00

    Hi Robert,

    The error "We couldn't update the system reserved partition" occurs if the EFI partition is full.

    Open Command Prompt (admin) and run these commands:

    cmd.exe

reg add "HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc" /v EspPaddingPercent /t REG_DWORD /d 0 /f

mountvol Y: /s

del  /q  Y:\EFI\Microsoft\Boot\Fonts\*.ttf

powershell -command "GCI Y:\  -File -Recurse | Sort Length -descending | Select FullName, Length, Mode -first 10"

dir Y:\

    Post the output here.

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