Windows Update KB5079473 - Updates Failed error 800f0991 - Standalone Installer say its already installed

Question

Windows update says KB5079473 failed to install error 800f0991. I tried to sfc /scannow, DISM cleanup-image restorehealth and startcomponentcleanup and it didn't resolve the issue.

I tried using Windows Update Standalone installer with files from the Windows update catalogue and it says the update is already installed.

Any idea how to resolve this?

Answer 1

Please try performing an In-place Upgrade. It will definitely help in resolving update errors. Performing this can repair broken operating system files while your personal files, settings and installed applications will not be removed.

Few things to check on the PC

• Unplug all external peripherals except for the Mouse, Keyboard, and LAN cable before starting
• Disable or uninstall any third-party Antivirus program to prevent it from interfering with the upgrade

https://learn.microsoft.com/en-us/answers/questions/4252110/how-to-run-in-place-upgrade-in-windows-11?forum=windows-all&referrer=answers

Answer 2

Just to be sure run the recovery option in Windows 11.

Settings > System > Recovery > Fix problems using windows update, select Reinstall now.

Answer 3

Hi, good day!

Open Settings > Windows Update > Update history

Please take a screenshot of the resulting window and post it in your next response.

Note: Don't include any personal information or sensitive data as Microsoft Q&A is a public forum.

I look forward to your update and am happy to continue working with you until the issue is resolved. If you find the answer helpful, please click "Accept Answer" and consider upvoting it. Otherwise, please keep me posted by clicking "Add comments" below instead of selecting Yes or No.

Answer 4

The behavior indicates that KB5079473 is partially or already installed, but Windows Update still reports a failure. In similar cases with KB5079473 and error 0x800f0991, the reliable fix has been to perform an in‑place repair/reinstall of Windows using current installation media.

An in‑place repair reinstall keeps personal files and apps but refreshes the Windows component store and update metadata, which clears the inconsistent state that causes KB5079473 to show as both failed and already installed.

Follow the steps in the Windows reinstall guidance to reinstall the current version of Windows, then run Windows Update again to confirm that KB5079473 no longer appears as failed.

If issues persist after reinstall, collect logs as described in the troubleshooting articles and contact Microsoft Support for further analysis.

---

References:

• Fix Windows Update corruptions and installation failures
• Windows Update troubleshooting guidance
• March 10, 2026—KB5079473 (OS Builds 26200.8037 and 26100.8037)
• KB5079473 fail with 0x80073712 while inplace upgrade fail with 0x8007042B - Microsoft Q&A
• Latest Security Update KB5079473 (26200.8037) Fails to Install - Microsoft Q&A