How to Fix Windows Update Error 0x800f0991 (Update Install Fails)
DISM.exe /Online /Cleanup-image /Restorehealth followed by sfc /scannow. If the update still fails, install it manually from the Microsoft Update Catalog using its KB number.What error 0x800f0991 means
Windows installs updates through a system called Component-Based Servicing, or CBS. Think of CBS as a project manager: it downloads the update packages, stages them, checks that everything the update needs is present, and then commits the changes to your system. Error 0x800f0991 is the manager reporting that the commit step failed. The update files are there, but something in the servicing machinery refused to apply them.
The most common root cause is damage to the component store itself — the database CBS relies on to stage and track updates. But the failure can also come from a corrupted download cache (each failed retry leaves broken files behind for the next attempt to trip on), a missing prerequisite such as a servicing stack update that the main update expects to find, or third-party software — especially antivirus — blocking Windows from replacing protected files during the commit. The steps below go from the least disruptive fix to the most thorough, in the order that solves the most cases.
Common causes
- Component store corruption: the CBS database that stages updates is damaged or inconsistent, so the installer cannot commit the changes. This is the number-one cause of 0x800f0991.
- Corrupted update cache: repeated failed attempts leave partial or mismatched packages in the SoftwareDistribution download folder, and every retry fails on the same broken files.
- Missing servicing prerequisite: some updates require a servicing stack update to be in place first; without it, the installer cannot sequence the install and aborts with 0x800f0991.
- Third-party interference: antivirus tools, system optimizers, or filter drivers can block file replacement while the update commits, causing the install to roll back with this error.
- Stalled services or a pending restart: update services that are hung, or an earlier update waiting on a restart, can leave the servicing pipeline in a state where no new update can commit.
How to fix error 0x800f0991 — step by step
Work through these fixes in order. Most people clear this error by step 4.
- Restart cleanly and retry the update once. A surprising number of 0x800f0991 cases are caused by a pending restart or a temporarily stuck service rather than real damage. Open Settings, go to Windows Update, and look for any pending restart warning. Restart the PC fully (not just sleep or hibernate), wait for it to settle, then click Check for updates and let it try once more. If it fails again, move on — repeating the same attempt is how the download cache gets more corrupted.
- Run the Windows Update troubleshooter. Go to Settings, then System, then Troubleshoot, then Other troubleshooters, and click Run next to Windows Update. The troubleshooter automatically restarts the update services, fixes incorrect service registrations, and clears minor cache problems. Let it finish completely, apply any fixes it recommends, and restart the PC before trying the update again.
- Clear the Windows Update download cache. Right-click Start, choose Terminal (Admin), and run
net stop wuauservandnet stop bits. Open File Explorer, navigate toC:\Windows\SoftwareDistribution\Download, select everything inside that folder, and delete it — leave the folder itself in place. Back in the terminal, runnet start wuauservandnet start bits, then check for updates. This removes partially downloaded or mismatched update packages that repeatedly fail at the commit step with 0x800f0991. - Repair the component store with DISM and SFC. Error 0x800f0991 is most closely tied to a damaged component store, the system the installer uses to stage and commit updates. In an admin terminal, run
DISM.exe /Online /Cleanup-image /Restorehealthand let it complete — this repairs the store from Windows Update. When it finishes, runsfc /scannowto fix any damaged system files. Restart the PC and retry the update. These two tools directly address the CBS servicing failures behind most 0x800f0991 cases. - Install the update manually from the Microsoft Update Catalog. If the built-in updater keeps failing, the problem may be the delivery pipeline rather than the update itself. Find the failed update's KB number in Settings > Windows Update > Update history, then search for that KB number at catalog.update.microsoft.com. Download the .msu file that matches your system (x64 for most PCs), double-click it, and let it install. A manual install skips the broken automatic download and often succeeds where Windows Update fails.
- Perform an in-place upgrade repair if nothing else works. Download the Windows Media Creation Tool from Microsoft, create an installation ISO for your version of Windows, and double-click it to mount the ISO. Run setup.exe from inside the mounted drive while Windows is running, and choose to keep personal files and apps when asked. This reinstalls Windows over itself, replacing the servicing stack and component store from clean media, and resolves stubborn 0x800f0991 failures that DISM and SFC cannot fix. Back up important files first as a precaution.
Did this fix it? Quick checklist
- Windows Update completes the update without showing 0x800f0991
- Settings > Windows Update reports that the system is up to date on the new build
- A follow-up
DISM.exe /Online /Cleanup-image /Scanhealthreports no component store corruption - The next Patch Tuesday update installs without repeating the error
If the error persists after all six steps, check how much free space is on the system drive — the servicing engine needs several gigabytes of working room to stage and commit an update, and critically low disk space can produce the same failure. Also try a clean boot (type msconfig, disable non-Microsoft startup items and services, restart) before retrying the update; this rules out third-party software blocking the commit. If a work PC is involved, ask the IT admin whether the machine is managed by group policy or WSUS — managed update pipelines can withhold prerequisites that the update expects, and only the admin can release them.
Frequently asked questions
What does Windows Update error 0x800f0991 mean?
Error 0x800f0991 means Windows Update downloaded an update but the servicing pipeline could not commit the install. The most common underlying cause is a damaged Windows component store, followed by a corrupted update cache, a missing prerequisite such as a servicing stack update, or interference from third-party security software.
Can DISM itself fail with 0x800f0991?
Yes. DISM's /Restorehealth uses the same component-based servicing engine as Windows Update, so it can report 0x800f0991 when the store damage is too deep for it to repair online. If DISM also fails with this code, run sfc /scannow first, retry, and then move to an in-place upgrade repair from Windows install media.
Why does 0x800f0991 keep coming back on every retry?
Each failed attempt leaves behind partially downloaded or mismatched packages in the SoftwareDistribution cache, so the next retry fails on the same broken files. Clear the download cache by stopping the Windows Update and BITS services, deleting the contents of C:\Windows\SoftwareDistribution\Download, and restarting the services before the next attempt.
Will I lose my files when fixing 0x800f0991?
No. Steps one through five touch only the update pipeline and system files — your documents, apps, and settings are not affected. Even the last resort, an in-place upgrade repair, keeps personal files and apps when you select that option. Still, a backup before major repair work is always good practice.