I’m a bit surprised Microsoft doesn’t have a guide for this one. It’s pretty easy to fix… we can pickle that!
In testing Console OS Lollipop for release, we ran into some issues with Windows 10 and Windows Update. The most common problem was updates would fail… and then attempt to reinstall at the next reboot. This would loop endlessly, consuming gigabytes of bandwidth. I feel really bad for people on capped Internet connections, because this could use dozens of gigabytes per month endlessly. And worse, Windows doesn’t even notify you (that it’s re-downloading each time).
The fix is pretty simple, takes a few steps.
Step 1: Run an Admin Command Prompt, and run chkdsk c: /f (followed by a reboot). Re-attempt Windows update.
Step 2: If that fails to fix it, run another Admin Command Prompt, and type sfc /scannow (this may take awhile). If it says some files were patched, re-run it, until it says all files verified successfully. If sfc reports that the files couldn’t be repaired, move on to the next step.
Step 3: In the same Admin Command Prompt, run DISM /Online /Cleanup-Image /RestoreHealth (this will take a long while, depending on your Internet connection). Then run sfc /scannow once again to make sure everything verifies (it should). Finally reboot, and run Windows Update once again.
Caution: Step 3 involves downloading a Windows restore image from Microsoft. You may not want to run it while on a metered connection. Windows metered connection checks don’t appear to run via this command.
The steps above will work on Windows 8 and above. Windows 7 and Windows Vista require a modified process, due to the lack of online image recovery mode.
Hope that helps folks. I don’t get paid to fix Windows, but it is part of my job. Sigh.