0x80070643 ERROR_INSTALL_FAILURE: Fix Windows Update Install Error

Fix Windows Update error 0x80070643 (ERROR_INSTALL_FAILURE) in Windows 10 and 11, including KB5034441 WinRE, .NET Framework, and Defender update failures.

Windows Update error 0x80070643 (ERROR_INSTALL_FAILURE) means an update downloaded correctly but failed while installing. It shows up most often with .NET Framework updates, Microsoft Defender definition updates, and the Windows Recovery Environment (WinRE) security update KB5034441. This guide explains each case and walks you through the fixes, starting with the quickest.

Quick answer: Restart your PC, run the Windows Update troubleshooter, then reset the Windows Update cache (Fix 3). If the failed update is KB5034441, see Fix 6, because that error comes from a WinRE partition that is too small.

What does error 0x80070643 mean?

The code 0x80070643 stands for ERROR_INSTALL_FAILURE, which means “Fatal error during installation.” Windows got the update files, but the installer stopped before it could finish.

You may see messages like:

• There were some problems installing updates... (0x80070643)
• 2024-01 Security Update for Windows 10 (KB5034441) - Error 0x80070643
• Security Intelligence Update for Microsoft Defender Antivirus - Error 0x80070643
• .NET Framework update failed - 0x80070643

Common causes

• WinRE recovery partition too small (the classic KB5034441 problem)
• Damaged .NET Framework installation
• Corrupted Windows Update cache
• Damaged system files
• Third-party antivirus conflicting with Microsoft Defender updates
• The Windows Installer service not running properly

How to fix error 0x80070643

Try the fixes in order. Restart your PC after each one and check Windows Update again.

Fix 1: Restart and retry the update

1. Restart your PC (choose Restart, not Shut down).
2. Go to Settings > Windows Update and select Check for updates or Retry.

Sometimes a pending installation blocks the next one, and a restart clears it.

Fix 2: Run the Windows Update troubleshooter

1. Open troubleshooter settings

   • Windows 11: Go to Settings > System > Troubleshoot > Other troubleshooters.
   • Windows 10: Go to Settings > Update & Security > Troubleshoot > Additional troubleshooters.
2. Run the Windows Update troubleshooter

   Select Run next to Windows Update and apply any fixes it suggests.

Fix 3: Reset Windows Update components

Clearing the update cache removes broken installer files.

Open Command Prompt as administrator and run these commands one by one:

Reset Windows Update

net stop wuauserv
net stop cryptSvc
net stop bits
net stop msiserver
ren C:\Windows\SoftwareDistribution SoftwareDistribution.old
ren C:\Windows\System32\catroot2 catroot2.old
net start wuauserv
net start cryptSvc
net start bits
net start msiserver

Restart your PC and check for updates.

Fix 4: Repair system files with DISM and SFC

Open Command Prompt as administrator and run:

Repair system files

DISM /Online /Cleanup-Image /RestoreHealth
sfc /scannow

Wait for both scans to finish, restart your PC, and try the update again.

Fix 5: Repair .NET Framework

If the failed update mentions .NET Framework, repair it first.

1. Download the repair tool

   Download the Microsoft .NET Framework Repair Tool from Microsoft’s official website.

2. Run the tool

   Run the tool, accept the terms, and let it apply the recommended fixes.

3. Turn .NET 3.5 off and on (optional)

   Press Win + R, type optionalfeatures, and press Enter. Uncheck .NET Framework 3.5, select OK, restart, then check it again and select OK.

4. Retry the update

   Restart your PC and run Windows Update again.

Fix 6: Fix KB5034441 (WinRE partition too small)

On Windows 10, the security update KB5034441 fails with 0x80070643 when the recovery (WinRE) partition does not have enough free space. Microsoft’s fix is to make that partition about 250 MB larger.

This fix changes disk partitions. Back up your important files first. If you are not comfortable with disk commands, skip this fix. The error does not harm your PC, and your other updates still install normally.

1. Check the WinRE status

   Open Command Prompt as administrator and run:

   reagentc /info
   

   Note the Windows RE location line. It shows the disk and partition number, for example harddisk0\partition4.

2. Disable WinRE

   reagentc /disable
   
3. Shrink the Windows partition by 250 MB

   Run diskpart, then:

   list disk
   sel disk 0
   list part
   sel part 3
   shrink desired=250 minimum=250
   

   Replace 0 with your OS disk and 3 with your Windows (C:) partition number.

4. Delete and recreate the recovery partition

   Still in diskpart, select the recovery partition and recreate it:

   sel part 4
   delete partition override
   create partition primary id=de94bba4-06d1-4d40-a16a-bfd50179d6ac
   gpt attributes=0x8000000000000001
   format quick fs=ntfs label="Windows RE tools"
   exit
   

   Replace 4 with your recovery partition number. On MBR disks, use create partition primary id=27 instead and skip the gpt attributes line.

5. Enable WinRE again

   reagentc /enable
   reagentc /info
   

   Check that Windows RE status shows Enabled, then run Windows Update again.

To check your disk type, run diskpart, then list disk. If there is an asterisk (*) under Gpt, your disk is GPT. Otherwise it is MBR.

Fix 7: Fix Microsoft Defender update failures

If the failed update is a Security Intelligence Update for Microsoft Defender:

1. Temporarily turn off or uninstall any third-party antivirus.
2. Open Windows Security > Virus & threat protection > Protection updates and select Check for updates.
3. If it still fails, open Command Prompt as administrator and run:

Update Defender definitions

"%ProgramFiles%\Windows Defender\MpCmdRun.exe" -RemoveDefinitions -DynamicSignatures
"%ProgramFiles%\Windows Defender\MpCmdRun.exe" -SignatureUpdate

Fix 8: Restart the Windows Installer service

1. Open Services

   Press Win + R, type services.msc, and press Enter.

2. Restart Windows Installer

   Find Windows Installer, right-click it, and select Start (or Restart if it is already running).

3. Retry the update

   Go back to Windows Update and try again.

Fix 9: Install the update manually

1. Find the KB number

   Go to Settings > Windows Update > Update history and note the KB number of the failed update.

2. Download from Microsoft Update Catalog

   Visit the Microsoft Update Catalog, search for the KB number, and download the version for your system (x64 or ARM64).

3. Install it

   Double-click the downloaded file and follow the prompts. Restart when asked.

How to prevent error 0x80070643

• Use only one antivirus program at a time.
• Keep at least 20 GB of free space on drive C:.
• Do not turn off your PC while updates are installing.
• Run DISM and sfc /scannow every few months to keep system files healthy.

Frequently asked questions

What is ERROR_INSTALL_FAILURE?

It is the internal name for error 0x80070643. It means an update was downloaded but failed during installation.

Why does KB5034441 fail with 0x80070643?

The recovery (WinRE) partition on your PC is too small for the update. Enlarging it by about 250 MB (Fix 6) solves the problem.

Is it safe to ignore error 0x80070643?

If it only affects KB5034441, your PC keeps working normally and other updates still install. For .NET or Defender updates, fix it so you keep getting security protection.

Will these fixes delete my files?

Fixes 1 to 5 and 7 to 9 do not touch your files. Fix 6 changes disk partitions, so back up your files before trying it.

Does 0x80070643 happen on Windows 11?

Yes. It can appear on both Windows 10 and Windows 11 for .NET and Defender updates. The KB5034441 WinRE issue mainly affects Windows 10.