Bricked OnePlus One can now be easily unbrick and go back to the stock firmware with a new application called OnePlus Recovery Tool. OnePlus One smartphone is currently running on the CyanogenMod 11 (Android 4.4.4 KitKat) ROM. However, if you have modified your device with a custom ROM or bricked it while doing so, OnePlus Recovery Tool can restore your device.
OnePlus Recovery Tool is a Windows only tool that makes it easy to restore OnePlus One to stock firmware (CM11). In addition, with this tool you can unbrick or fix any problems you may run into your phone. Created by the XDA member Zyxxeil, this application is somewhat simple to use.
In this guide, we will let you know how to use OnePlus Recovery Tool to restore your OnePlus One to stock and unbrick it.
1. Download OnePlus Recovery Tool for 16GB or 64 GB OnePlus One [Download appropriate one here]
2. Run the application with administrative privilege (right click and select “run as administrator”).
3. Switch off your phone and connect it to your PC via USB cable. Now, hold Volume UP + Power together.
3. Your computer should detect your phone. If your device is not detected, install correct drivers. Still not detected, install the QPST tool.
4. Click Refresh and then click Start (Make sure Normal Restore is checked)
5. It will flash the stock ROM (It will take little long time to complete the flashing process, so do not interrupt the flashing process)
6. Once the process is done, it will show green.
Now, disconnect your OnePlus One from your PC and reboot it. It should be now fully restored to stock CM11s. Enjoy! (Source – XDA)