Update fails to install

Error 0x800f0845 is not currently listed by Microsoft as a known KB5127648 installation issue, so repair the Windows servicing components with DISM and SFC, restart, and retry the update.

KB5127648 is applicable to Windows 11 25H2 build 26200 and should update it to 26200.9711.^1^ The published known-issues section does not identify an installation failure involving 0x800f0845, so that code alone does not establish the exact cause.

1. Repair Windows components

1. Search for Command Prompt.
2. Right-click it and select Run as administrator.
3. Run these commands in this order:

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

Do not close the window until SFC reaches 100%. DISM repairs the Windows component image first; SFC then checks and replaces damaged protected system files.^2^

4. Restart the PC.
5. Open Settings > Windows Update > Check for updates and try KB5127648 again.

If DISM reports that source files could not be found, do not continue repeatedly retrying Windows Update; proceed to the repair reinstall below.

2. If it still fails, install the complete standalone package set

KB5127648 uses a checkpoint cumulative update. A manual installation must include the required checkpoint and install the files in Microsoft’s specified order; installing only the final KB package can fail.^3^

1. Open Settings > System > About.
2. Under System type, determine whether the PC is x64 or ARM64.
3. Open the Microsoft Update Catalog from the KB5127648 article and download all packages listed for that architecture.
4. Put them in an empty folder.
5. Double-click the files in the documented order:
   1. Required checkpoint cumulative update KB5043080
   2. Target cumulative update KB5127648
6. Restart and check Settings > Windows Update > Update history.

If Windows says KB5043080 is already installed, continue with KB5127648.

3. Non-destructive repair reinstall

If both Windows Update and the standalone packages fail, use Windows 11’s built-in repair reinstall:

1. Back up important files.
2. Open Settings > System > Recovery.
3. Under Fix problems using Windows Update, select Reinstall now.
4. Keep the computer connected to power and the internet.
5. Restart when prompted, then check for updates again.

This reinstalls the same Windows version, repairs system files and components, and preserves installed apps, files, and settings.^4^

Check the Windows channel

Build 26200 identifies Windows 11 version 25H2, but it does not by itself determine whether the device is enrolled in an Insider channel. Check Settings > Windows Update > Windows Insider Program:

• If the page says the device is not enrolled, it is using the normal servicing channel.
• If it shows Release Preview, Beta, or another Insider selection, note that channel before escalating.

If the repair reinstall also fails, provide Microsoft Support with the current build from winver, the channel shown on that page, and the latest failure time from Windows Update > Update history.

References

1. October 13, 2026—KB5127648 (OS Builds 26300.9711, 26200.9711 and 26100. ...
2. Use the System File Checker tool to repair missing or corrupted system files | Microsoft Support
3. [Microsoft Update Catalog](https://support.microsoft.com/servicing/os/windows-11/2026/10/kb5127648-windows-11-24h2-25h2-26h2-security-update)
4. Fix issues by reinstalling the current version of Windows | Microsoft Support