[Xperia Z1 General] nickcaper:
Yea there is a guide..

I made it for you now.

The following guide will help new Sony Xperia Z users to restore handsets to original factory firmware.

Note: This tutorial does not require you to root your handset nor does it require you to unlock your bootloader.

FLASHING YOUR HANDSET DOES NOT VOID YOUR WARRANTY.

PREPARATION

Make sure your phone is charged.

1) Download and install Flashtool

2)Download and install the Flashtool drivers

When install, take heed, this is a 3 step process to make complete use of the drivers. If you dont install all 3 drivers the whole process will be useless.

On first round of install choose the "Xperia Z1" driver which in my case is for the C6916. Not sure which driver you will need for YOUR phone. DO research.

After that, reopen the tool again and scroll down to install Flashmode drivers. Then yet again after this install, open the tool once more to install the flash boot drivers. These drivers are for when you put the phone in certain modes that your computer may recognize them so you can install FTF backups.

3)Download the FTF for your C6916 HERE.. This is specific to this phone only. Its the latest factory Rom. C6916_14.4.B.0.37_T-Mobile.ftf

4)Enable USB debugging

Settings => About phone => Click 7 times on Android Build to unlock developer options

goto security, check on Unknown sources enabled

make sure adb drivers are installed

FTF INSTALLATION

1) Make sure you connect your Xperia to the PC through a USB Port.

This is important because the phone screen will create a popup which will ask you if the installation is good to go from YOUR computer! You MUST see this pop on your phone and acknowledge it before installation can occur.

2) Place firmware in correct location on your PC. This means, on the same Hard drive as the one you installed the Flashtool onto. Not an external drive. Place the FTF file in the C:\Flashtool\firmwares folder. You will know it is properly saved in the correct file because Flashtool will show it as an available update INSIDE the program itself. Usually there may be a X10 FTF that is by default always there. You can ignore that FTF or even delete it.

3) Launch Flashtool

Open the Flashtool application on your PC.

Click on the lightning bolt symbol. Select Flashmode and click OK.

4) Select firmware (click on it to highlight it) which should already be available (if you put it in the correct folder)

If you do not want to do a clean install ensure ‘Data’ is not ticked. Press the ‘Flash’ button.

Note: For the Xperia Z, internal storage and data storage are in the same partition. Therefore wiping data will erase everything including media. As a precaution, we recommend backing up all content.

5) Connect your Xperia to the PC

Once you press the Flash button, you will see that Flashtool is ‘Preparing files for flashing’.

At some point a Flashtool window will appear on your PC and tell you to unplug your phone. This is where you MUST invoke FlashMode on your phone.

I have found that I must do this manually.

Turn your phone off. Unplug from USB Port. While the phone is off and unplugged from usb port, press and hold the volume down, holding this button, then plugging the USB cable into your Xperia.

6) Flashing process will start

You will see the Flashtool start to flash the FTF to the phone. It may take upto 5 minutes. DO NOT unplug the phone until Flashtool says too.

Once you see the “Flashing finished” message in Flashtool, remove your handset from the PC and restart it (this may take a few minutes so don’t panic).

7) Your Xperia Z should now be with a fresh install of Factory Firmware.

The 2 different "MODES" of the experia Z during boot up.

Fastboot mode----(Blue LED, )Switch the phone OFF , hold the volume UP button while you plug-in the USB. (DO NOT PRESS POWER!)

Flash mode -----(Green LED), Switch the phone OFF , hold the volume DOWN button while you plug-in the USB. (DO NOT PRESS POWER!)

How bout you share with us how you root with EasyRoot AFTER the OTA... Cause I just tried.. its stops at "creating vm"