How to fix Windows update error 0x800F0840?

Error 0x800f0840 means the Windows servicing stack could not load the saved record of an update session, so the update stops and rolls back. It usually follows an update that was interrupted or never finished its restart. Restart the PC properly and check for updates again, then repair the component store with DISM and SFC.

Facts checked on 15 October 2026. Steps written for Windows 11 (25H2 and 26H2) and Windows 10 22H2.

What Windows update error 0x800f0840 means

0x800f0840 belongs to the Component Based Servicing (CBS) family of codes, the 0x800f08xx range. CBS is the part of Windows that installs updates, features and language packs. The code's name, as CBS.log writes it, is CBS_E_SESSION_CORRUPT.

Each update runs as a servicing session. Windows saves the state of that session to disk, so the work can continue after a restart. When Windows later tries to load that saved state and finds it damaged, the update stops with 0x800f0840 and Windows undoes the changes.

Why error 0x800f0840 appears

The causes are ordered from the most likely to the least likely. The order comes from what the code means and from the reports we read. Microsoft has not published a list of causes for this one code.

The Qualys support article about 0x800F0840 in patch jobs ties the code to the same three things: damaged system files, an inconsistent Windows image, and earlier update installs that went wrong. It also notes that the failing updates in its case needed a restart to finish.

How to fix Windows update error 0x800f0840

Fix 1 costs nothing and clears a session that only needs its restart. Fix 2 and Fix 3 repair the store and the update cache, which is what support teams recommend for this code. Fix 4 to Fix 6 are for the cases where one update or every update keeps failing.

Fix 1. Restart the PC properly and check for updates again

5 to 15 minutesNo riskEveryone first, and above all when the PC was switched off during an update or shows Restart required.

A servicing session that waits for its restart cannot be loaded cleanly by the next update. A real restart lets Windows finish or discard that session, and the next attempt starts a new one.

1. Save your work and plug in a laptop.
2. Open Start, select the power button and choose Update and restart if it is there, otherwise Restart. Do not use Shut down.
3. Wait until Working on updates reaches 100 % and the sign in screen appears. Do not press the power button while it works.
4. Restart a second time, so that any work that needed two restarts is done.
5. Open Settings > Windows Update and select Check for updates.
6. Install what is offered and restart again when Windows asks.

Fix 2. Repair the component store with DISM and SFC

15 to 40 minutesNo riskThe same update still fails after two restarts, or the PC lost power during an earlier update.

0x800f0840 means servicing data could not be read. Microsoft's advice for a damaged component store is DISM RestoreHealth, which downloads clean copies, followed by SFC. The Qualys article gives the same repair for this code.

1. Open an elevated command window. Right-click Start and select Terminal (Admin), or type cmd in the search box, right-click Command Prompt and select Run as administrator. Select Yes when Windows asks for permission.

   

2. Run DISM first. Type the command below and press Enter. DISM downloads clean copies of damaged components from Windows Update, so it can take several minutes. Wait until it says The operation completed successfully.

   DISM.exe /Online /Cleanup-Image /RestoreHealth

   

3. Run System File Checker. In the same window, type the command below and press Enter. Do not close the window until the verification reaches 100%.

   sfc /scannow

   

4. Read the result and restart. Compare the last message with the table below this guide, then restart the PC so that repaired files are loaded.

   

These steps were written for Windows 11 24H2 and 25H2. The full page with the other versions and what each result means: Run DISM and SFC to repair Windows system files

Fix 3. Reset the Windows Update components

10 minutesLow riskDISM and SFC report no problems, and Windows Update keeps failing at the same point.

Windows Update keeps the files it downloaded in SoftwareDistribution and reuses them at every retry. Renaming that folder and catroot2 makes Windows download the update again and start a fresh session. Qualys lists this reset as a step for 0x800F0840.

1. Open Command Prompt as administrator. Type cmd in the search box, right-click Command Prompt and select Run as administrator. Select Yes when Windows asks for permission.
2. Stop the update services. Type the commands below and press Enter after each one. If Windows says that other services depend on Cryptographic Services, it stops them too. A message that a service is not started is fine.

   net stop wuauserv
   net stop bits
   net stop cryptsvc

3. Delete the download queue files. This clears the list of downloads that the Background Intelligent Transfer Service keeps. If Windows says it cannot find the files, continue.

   del "%ALLUSERSPROFILE%\Application Data\Microsoft\Network\Downloader\qmgr*.dat"

4. Rename the update cache folders. Renaming keeps a copy in case you need it; Windows creates new, empty folders when the services start again. If you get Access is denied, a service is still running: repeat the previous step.

   ren %systemroot%\SoftwareDistribution SoftwareDistribution.old
   ren %systemroot%\System32\catroot2 catroot2.old

5. Start the services again. Type the commands below and press Enter after each one. The requested service has already been started is fine: Windows started it on its own.

   net start cryptsvc
   net start bits
   net start wuauserv

6. Restart and check for updates. Restart the PC. Then select Start > Settings > Windows Update > Check for updates. The first check can take longer than usual because everything is downloaded again.

These steps were written for Windows 11 and Windows 10 (the steps are the same). The full page with the other versions and what each result means: Reset Windows Update components

Fix 4. Install the failing update by hand from the Microsoft Update Catalog

15 to 30 minutesLow riskOne KB keeps failing while other updates install, or Windows Update cannot finish the download.

A .msu file from the catalog installs the package directly, outside the Windows Update download and its cache. If the package installs this way, the problem was in the update path rather than in Windows itself.

1. Check your Windows version. Press Windows key + R, type winver and press Enter. Note the version (for example 25H2) and the OS build.
2. Find the KB number. Open Settings > Windows Update. A failed or pending update is listed with its KB number; earlier ones are under Update history.
3. Check the processor type. Open Settings > System > About and look at System type: an x64-based PC needs the x64 file, an ARM-based PC (for example Snapdragon) needs the arm64 file.
4. Search the catalog. Open the Microsoft Update Catalog at catalog.update.microsoft.com in your browser, type the KB number (for example KB5124010) in the search box and press Enter.
5. Pick the right row. Find the row whose title names your Windows version and your processor type (x64-based or arm64-based) and select Download on that row.
6. Download every file listed. A window lists one or more .msu links. Download all of them into one empty folder, for example C:\packages. On Windows 11 24H2 and later the list can include earlier checkpoint updates that the new one needs.
7. Install a single file. If there is only one file, double-click it and confirm the installation in the Windows Update Standalone Installer.
8. Install several files with DISM. If there are several files, open an elevated Terminal or Command Prompt and run DISM with the newest file. DISM finds the other files in the same folder and installs them in the right order.

   DISM /Online /Add-Package /PackagePath:C:\packages\<newest-file>.msu

9. Restart. Restart the PC when the installation finishes, then run winver again: the OS build should have changed.

These steps were written for Windows 11 24H2 and later; Windows 10 22H2. The full page with the other versions and what each result means: Install an update from the Microsoft Update Catalog

Fix 5. Check the system drive for errors

10 minutes to 1 hourLow riskThe PC froze, crashed or lost power during an update, or other files are damaged too.

A session record is a file on the system drive. If the drive has file system errors after a power loss, the record can be damaged again after every repair. chkdsk fixes the file system first, so the repairs in Fix 2 hold.

1. Open Command Prompt as administrator. Type cmd in the search box on the taskbar, right-click Command Prompt and select Run as administrator. Select Yes when Windows asks for permission.
2. Scan the drive without changing anything. Type the command below and press Enter. Replace C: with another drive letter to check that drive. This scan only reports; it does not fix anything.

   chkdsk C:

   

3. If errors were found, run the repair. Run chkdsk with /f to fix file system errors. On the Windows drive (C:) chkdsk cannot lock the drive while Windows is running, so it offers to check it at the next restart.

   chkdsk C: /f

   

4. Schedule the check and restart. Type Y and press Enter, then restart the PC. chkdsk runs before Windows starts. Do not turn the PC off while it runs.
5. Read the result after the restart. The report of a check made at startup is not shown on the desktop. Open PowerShell and run the command below to see it, or open Event Viewer (eventvwr.msc) > Windows Logs > Application and filter by the sources Chkdsk and Wininit.

   Get-WinEvent -FilterHashtable @{LogName='Application'} | Where-Object { $_.ProviderName -match 'wininit' } | Select-Object -First 1 | Format-List TimeCreated, Message

These steps were written for Windows 11 and Windows 10 (the steps are the same). The full page with the other versions and what each result means: Check a disk for errors (chkdsk)

Fix 6. Reinstall Windows over itself and keep your apps and files

1 to 2 hoursLow riskEvery cumulative update fails with 0x800f0840 and Fix 1 to Fix 5 did not help.

A repair reinstall writes a clean copy of the current Windows version, including a new component store and new servicing data. The damaged session records are gone afterwards, while apps, files and settings stay.

1. Open Recovery in Settings. Open Settings > System > Recovery. Next to Fix problems using Windows Update, select Reinstall now. This keeps your apps, files and settings.

   

2. Start the reinstall. Choose whether the PC may restart on its own 15 minutes after the installation, then select OK.
3. Wait and restart. Windows Update downloads and installs a repair copy of your current Windows version. Keep the PC plugged in and online, and restart it when asked.

These steps were written for Windows 11 22H2 and later. The full page with the other versions and what each result means: Reinstall Windows without losing files

If Fix problems using Windows Update is missing, download the installation media of your Windows version from Microsoft, run setup.exe and keep the choice Keep personal files and apps.

If error 0x800f0840 is still there

Before you try anything else, read the servicing log. Microsoft's own advice for CBS errors is to open the newest CBS.log, search for the error and read the lines around the time of the failure.

1. Press Win + R, type %windir%\Logs\CBS and press Enter.
2. Copy CBS.log to the Desktop and open the copy in Notepad.
3. Press Ctrl + F and search for 0x800f0840. Note the time of the last hit.
4. Read the lines just above it. Failed to load session confirms a damaged session record. A KB number or a file name tells you which update or file is involved.

How to keep error 0x800f0840 from coming back

If the PC often loses power, a small UPS for a desktop is worth more than any repair. Most session damage starts with an update that was cut off halfway.

Frequently asked questions

What does error 0x800f0840 mean?

It means the Windows servicing stack could not load the saved record of an update session. CBS.log names the code CBS_E_SESSION_CORRUPT. Windows saves each update's progress so it can continue after a restart, and when that saved state is damaged, the update stops and rolls back. It most often follows an update that was interrupted or a restart that never happened. Restart properly first, then repair the component store with DISM and SFC.

Why does 0x800f0840 show up as failed to install every time?

Because Windows retries with the same damaged data. If the session record or the downloaded files are broken, each new attempt reads the same broken state and fails at the same point. That is why the error does not go away by itself. Two full restarts, then DISM RestoreHealth and SFC, and then a reset of the Windows Update cache give the next attempt clean data to work with.

Is it safe to keep using the PC with this error?

Yes, for a short time. The error does not damage personal files and Windows keeps running on the last installed update. The risk is missing security fixes, which matters more each week the update stays uninstalled. Work through Fix 1 to Fix 3 within a few days. If you cannot fix it, install the update by hand from the Microsoft Update Catalog, as described in Fix 4.

Can I fix 0x800f0840 by turning off my antivirus?

No source we read ties this code to security software, and turning protection off leaves the PC exposed. The code points to damaged servicing data, which antivirus does not repair. Use the fixes on this page in order. If you suspect another program blocks updates in general, test with a clean boot rather than removing protection, and turn everything back on afterwards.

Are 0x800f0841, 0x800f0843 and 0x800f0845 the same error?

No. They are neighbouring codes in the same CBS family, 0x800f08xx, and each has its own meaning. We did not verify those meanings for this page, so we do not describe them here. They often respond to the same first repairs: a proper restart, DISM RestoreHealth with SFC, and a reset of the update cache. Read CBS.log to see the exact code and the lines around it before going further.

Which updates fail with 0x800f0840?

Any cumulative or security update can, because the code is about the servicing session, not about one package. Reports name Windows Server 2019 with KB5016623 in August 2022, and the April 2025 updates KB5053643 and KB5055518 in a patch tool's job log. A search for kb5099538 also leads here. Whatever the KB number, the steps on this page are the same.

What does We couldn't finish the update. Undoing changes. have to do with 0x800f0840?

That screen appears when an update fails during the restart and Windows rolls it back. Users report seeing 0x800f0840 in Update history after it, sometimes together with other codes. The rollback itself is normal and protects the PC. If it happens again and again, the session data is damaged, and Fix 2 and Fix 3 are the steps that address it.

Will I lose files if I reinstall Windows to fix this?

Not with the repair reinstall in Fix 6. Fix problems using Windows Update, and Windows Setup with Keep personal files and apps, reinstall the same Windows version and keep apps, files and settings. Reset this PC with Keep my files is different: it keeps your files but removes installed apps. Back up the files you cannot lose before any reinstall, and keep a laptop plugged in.

A que se debe este error, lỗi gì đây, ايه المشكلة: what causes this error?

These searches all ask what causes 0x800f0840. The answer is the same in every language: Windows could not read the saved record of an update, usually after an interrupted update or a missed restart. The code is the same on Windows in any language. The menu names in the steps are the English ones, so follow the position of the items in Settings. The commands are typed the same way everywhere.