What's new

Unsolvable bootloop and error 21 issue

oliver howard

New Member
Nov 16, 2014
Reaction score
Hi to all,

Traded in my 4s for a second hand 5 with a "battery issue". Replaced battery and charging port and phone will still only react when plugged in at mains or usb but is stuck in bootloop. It can be discovered in itunes when in DFU, any attempts to restore just lead to error 21.

Hours of trawling through forums leads me to believe this can be caused by an infected file from jailbreaking? I think I have exhausted all of the obvious solutions - hard reset, holding volume up etc... I have also tried to access files using iexplorer and ifunbox but neither program will recognize that a device is connected. I have been advised elsewhere to try downloading pangu or evasion and rejailbreaking - I have tried both but to no avail as neither program will find the device connected.

Is there something obvious I haven't tried? It's incredibly frustrating. Thanks in advance for any help!
Error 21 comes from attempting to use TinyUmbrella as a TSS bridge on an unsupported device such as the iPhone 5 or attempting to use a custom firmware without placing your device into Pwned DFU mode (does not apply for the iPhone 5). Jailbreaking a device does not modify the boot chain and does not affect the battery in any way. Start afresh with iTunes. Uninstall it with all its components, hard reboot your computer, reinstall the latest version of iTunes, check your host file to see that Apple is not blocked, if it is, remove it from your host file and flush your DNS, plug the device back into your computer and DFU it again.
Thanks for your help.
Apologies I didn't mean the jailbreaking affecting the boot process but rather an infected or corrupt app that could have been installed?
I will try uninstalling itunes and all its components and keep my fingers crossed. Do you know where I can get a list of all applicable components?
Thanks again
Mainly anything that has Apple in the distributor/company name. Mainly uninstall Quicktime, iTunes, Bonjour and anything Apple in its name. If you've made backups that you want to keep, you might want to move them to a new location as they're wiped when iTunes is removed AFAIK.
Only just got round to trying this. Still no luck unfortuantely - although slightly different response this time. Itunes seemed to stall once it got to "waiting for iPhone", phone booted up into the loop, then itunes revealed error 4005...not had that one before but guessing it's down to the lack of response from the phone.

I fear I may have a paperweight here...
Error 4000s are from lost of communication with the device during the restore process. If you have another cable, try it on the same computer. If you have another computer, use that computer. If you only have access to one computer, create a separate administrative user, and install iTunes through that administrative account and re-attempt. Bricks are either error -1 or certain hex errors.