Endless boot loop on 435 after the spinning gears - Build 10166


I have a serious issue when installing the latest fast ring build 10166. In few words, it downloads the build, prepares to install and the spinning gears are shown normally. But, at the end of the process in the spinning gears phase, the phone simply shutdown and not restart itself automatically. So, I turn on the phone manually, and after the Microsoft logo, it shows again the spinning gears, but this time they spin for about 1 minute, and after this time the phone restart itself, and if I don't turn off the phone, it keeps rebooting again and again in an endless boot loop state. I've reverted back to 8.1 and tried again to update to build 10166, but I had the same identical problem as before, so now I had to return to 8.1 and stay at 8.1, because of this serious issue.

I have a Lumia 435 CV IT and the revision of firmware is 02074.00000.15234.28005


We've figured out the issue.  You all are on the right track here.

Originally, the 435 was slated to be a 4GB device.  The change to having 8GB of disk space was made very close to launch and the devices were re-configured as such.

What's driving the boot loop issue is how the OS is compressed/decompressed.  When Win10 is unpacking, it's reading several characteristics from the device and metering disk space usage accordingly.  The API that is handling the new OS install is un-compessing the OS early and the the device is hitting a disk space conflict.  This is the only device to end up in this particular situation as it was the only device produced where this disk space sizing change was made.

Our Engineering teams have already developed the appropriate code to address this issue, but as you can imagine it won't be available until we release a future preview build.  As such, there's no current workaround for users.

What should you do?

First up:  everyone affected should use the WPRT and recover back to 8.1.  It's the only way to get the device back into a usable state.  After that, you have two options:

1)  After 8.1 installs, during OOBE, don't restore your backup or any personal data.  This will help save disk space.  Also uncheck the box for apps to auto-update.  As soon as you're on the Start screen for 8.1, re-download the Insider app and try to get to Win10 again.  This *IS NOT* guaranteed to work, but taking these steps may save enough space to allow the device to use partition stitching and take the update.  Again, this is not guaranteed to work, but for some 435 variants, you may have success.

2)  Go through 8.1 OOBE as normal and wait for the next preview build to be released.  This is the bucket most 435 users will end up in.  It's unfortunate, we know.  Good thing is we found this bug now and are already addressing it.  We should have affected users back in the saddle without too much delay.

And before anyone asks:  I don't have any comments on when the next build will be released.  Stay tuned to Gabe's blog for that info.  :)

Wish I had better news.  On the good side, it was your direct feedback that helped us uncover this and figure it out this quickly.  Can't thank you all enough for being Insiders.  The efforts you put forth are always appreciated.

Thank you,

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Question Info

Last updated January 28, 2021 Views 1,316 Applies to: