Recover iPad from failed OS update (error 1604)

Recently I've been setting up a set of iPads for a client and Apple released the latest update to their iOS. So as part of the setup I installed the update to each iPad. Unfortunately three of them failed and refused to start afterwards. When I connected them to the laptop with iTunes on it, a message popped up informing me that there were several iPads in a recovery state that needed to be restored from a backup (error 1604). I attempted this several times and each time it failed.

After some time spent on Google hunting around for a solution, I finally found an answer to my problem. It turns out that iPads have two recovery modes; standard recovery mode and DFU (Device Firmware Upgrade) mode. In DFU mode the iPad doesn't load any operating system or boot loader when it connects to iTunes. This enables you to restore a working version of iOS to the iPad and then complete a restore through iTunes.

In order to get your iPad into DFU mode you need to follow the steps below:

1. Load iTunes on your laptop/PC/Mac
2. Connect your iPad via the USB connector
3. Press and hold the power button and home button on your iPad for 10 seconds. It must be 10 seconds precisely or this will not work.
4. After 10 seconds release the power button but continue to hold down the home button for a further 5 seconds.

If done correctly your iPad screen should remain blank and iTunes will report a device in recovery mode. Under Windows you will also get a notification that the DFU recovery driver has been installed for your device. You can then complete a restore of the device and settings through iTunes. If your iPad screen does not remain blank then you haven't done it properly and need to try again. It's fiddly but it does work once you get the knack of it.