Thanks guys to let this threat live again, I had lot of replys thanks to this post!!!
For all the replys about how to check your Xperia Z1 version, with this simple method, you dont need to turn on the device and starting wasting your time, this method is free battery consuming (think about the case, your battery is completed dead and you cant turn on your device) , free code combinations, dont need to turn on the device, so you can start flashing your device right away.
I hope that new people fix their devices, usually the Z1 is problem free if you dont:
-Dont remove the charger or sd card cover too much (I use the chinese version of the magnetic adapter from 1 year and going strong, also I just updated the quick charger and IT IS GOOD)
-If you use it on the beach and not clean the device with normal water
-If you tweak too much the device (optimizer apps, some weird things with power management of the processor)
AND NO GUYS ,I DONT WORK FOR SONY, i just own one and I know what I have, but I must say this new Kitkat with SD limitation, is filling up a little the internal storage, having a 64gb micro sd on the device.