Share your experience!
My xperia z is quickly heating everytime use it. Especially it heats up very quickly during Navigation use, battery charging etc. Any idea the reason for this. I would appreciate if you can give me a solution to avoid this.
Which country do you live?
UK
It's rather rainy then, good to choose water-resistant phone 
Please take into account considering heat issues every time when it comes to buying high end, quad core processor device as it refers to all devices representing similar segment.
Manufacturer claims it is fine and basically should be right.
The processor combined with Android OS is equipped with anti overheating solutions which means to the user that if the temperature will raise too much (over established level) it will start to close heavy and processor demanding apps first, as well as device will be shutted down for a while due to cooling purpose and security reasons in case it will not help.
If I am not wrong, you should be warned by the system before the above procedure will take place.
Honestly, I was playing with GS4 and HTC one as well and under heavy usage the devices became even hotter than Xperia Z. I assume Sony provided better cooling solution in this model (probably more carbon).
However, if my explanation cannot be considered as helpful and still you think something is wrong with your device I suggest to deliver it to the closest Sony Service Center and check it.
i have both devices, the Z and the S4, and must say, the Z gets much more hot than the S4.
In my opinion S4 is hotter, but this will always be subjective.
it's normal that it gets hot due to screen, since FULL HD screen can make phone hot easly so nothing to worry about 
Thanks for your replies guys. However, One of my friends got the same phone but he hasn't got this kind of issue as far as he is aware(may get in the future never know:smileywink:). When I spoke to the network providers today they are saying, it is quite normal that may heatup while charging but not usually does quickly when we are using Navigation, apps etc.as I am facing now and recommended me to contact sony for the right advice.
Also, one issue which is very silly is, it is also heating up when I talk just for half an hour on the phone. I think it is not usual(I might be wrong) as I didn't get this problem with my previous phone(iphone 3G, 4 etc).
If it heats up that quick whilst on the phone, I think it is not certainly meant to be an ideal piece to use as a mobile phone as the effect of the phone radiation may have direct impact on our body and brain.
reason why you didnt get it on iphone 3g, 4 etc thats because they werent any FULL HD displays on them, so sony xperia z gets hot when you play games on it, watch videos, and so so due to FULL HD screen.