My just upgraded iPhone 5S ( 8.0.2 ) is suffering from over-heating and all the apps are crashing ... I had to cancel my call just after 10 minutes as it was so heated up ...

You aren't speaking to Apple by posting here. This forum is a user-to-user technical support forum and if you want to contact Apple, you'll need to use the Contact Us links at the bottom of every page. Or make an appointment at your nearest Genius Bar to have the device evaluated.

Just begun happening for me, but only with iBooks on my iPhone 5S. Updated to 8.0.2. on Sunday morning and all fine Sunday and Monday. This morning I purchased a book from iTunes and began to read it, three pages in and device crashed. I re-booted (held on and off buttons) re-opened and read a bit more, crashed again. Then realised how hot the phone was so I turned the phone off completely, left it to cool, turned on again and tried to read the book. Felt the heat start again, thought maybe just that book was a problem so deleted it, turned phone off and let it cool. Tried another book once phone was on again and it took longer to begin to heat but definitely started getting hot again. I also noticed a massive drop in battery (from around 67% to 17% in around an hour.

Download was done via 4G and I noticed it was a hesitant download - got to about 3/4 and kept flashing to the cloud symbol and then the download ring. Tested other apps and no problem (Facebook, Twitter, a card game, App Store, mBox mail, kindle to name a few)

Currently re-charging the phone so will wait until that is done before attempting anything else.

Note my iPad Mini and iPod Touch 5th gen have no problems (so far).

There's another thread more or less covering this problem - I've also put my details on that so it may also be worth your joining in there.

There's a few comments on there that may help, I'm charging my phone at the moment so can't take any action suggested but read through from page 1 to the end before trying anything, then see if any of the suggestions fit your problem.

In my case it just seems to be ibooks causing the heating and crashing - note I don't use iCloud, I do everything via PC or direct download to device.

iPhone 5S getting incredibly hot and high battery usage after iOS 8 update

The heat is caused by the processor or radio (LTE) chips running at full power for an extended time. I do know that the A8 chip runs cooler than the A6 or A7, so they can run at full speed longer without overheating. I'd be curious to see if it isn't detecting the chip incorrectly and running at full power. More often than not, overheating comes from a process hanging in a circular logic loop. The iPhone does multitasking, which means even if the foreground app is working fine one of the background apps may actually be the cause. You can try turning off Background Update for all the applications and see if it gets better.
If you can't get that far, you should consider back-leveling the OS to 8.0.0 or even 7.x - you can do so through iTunes and either restore to factory or restore from backup. Restoring to factory is a good test to see if the problem remains. If with no applications installed the phone works correctly then you know it's not the OS. If it continues to overheat, then you may want to consider back-leveling to 7.x until a few more iterations come out. There are not substantial user interface differences between 7.x and 8.x, and most of the new APIs are not yet widely in use. You really won't see much difference until more apps utilize HealthKit, Metal and so on.

I don't have background update turned on, and tried closing all apps before re-opening ibooks but made no difference. I'm charging via battery doctor which has just finished. (I have most battery hungry items turned off such as location, push notifications).

Prior to downloading the e-book I had updated (via 4G) twitter, Amazon, Creative Cloud Tutorials and Panasonic Smartphone Connect (info probably of little relevance but adding it here in case it is needed later).

Whilst charging I checked the battery usage for the last 24 hours and it showed 40% for iBooks - and I only had iBooks open this morning when I downloaded that book and attempted to stop the heating. It's now showing 41% even though the app is closed. The other apps the battery usage shows are pretty much as I would expect from the usage I made in the last 24 hours.

I'm backing the phone up now (having backed up the mobilesynch folder in case I need to revert to an earlier backup. I notice it is copying diagnostic information - not seen a back up do that before but I don't usually watch the progress. Back later if I have any further to add.

I've now opened several apps and used for maybe 5 minutes with no problem - Facebook, Echefon for Twitter, Kindle, Solitaire, mbox mail, the app store, Mulberry, Safari (BBC News). iPlayer needed updating and I had already downloaded that to computer so synched phone again, although the app transferred I still had a badge on home screen showing 1 app to update, and visiting app store page initially showed iPlayer needed updating but rapidly switched to the 'open' box.

I then opened ibooks and within seconds the phone was becoming hot - if only iBooks were not now part of the OS I could have removed and reinstalled the app to see if that resolved the problem. I'm now loathe to add any books to the app on my iPad or iPod Touch in case the same happens (probably won't as I've only seen comments on here about 5S and some 6plus heating).

Still happening with ibooks on my iPhone, have just tried to replicate this on my iPad mini by adding all the updated apps so it matches the iPhone, and then the same book. There's a slight heat to the rear of the ipad but very slight, whereas on the iPhone it is hot enough that I feel I need to turn the phone off and not use it. During the day I've made a conscious effort to use apps on the phone and no problem with those. Reading from ibooks on the iPod Touch (which has not had today's app updates added, nor the book I downloaded) no problem at all.

I opened a book on the iPhone at 20.39 with 96% battery. App crashed at 20.40 at 95% battery. Opened again, no crash but by 20.43 battery read 92%.

A quick look at battery usage shows today 43% but for the past 7 days only 10% of total battery power used.

In comparison Echofon which I use a reasonable amount shows 14% today and 32% over 7 days/Facebook 6% today 9% over last 7 days/Mail 4% today (says low signal below the app name) 7% over 7 days. I haven't used the phone much this week as I've been home a lot of the time (not working at the moment) and only used the phone for data when out and about.

All my devices have 8.0.2 - guess it's a problem with the phone software rather than iPad or iPod Touch.

Woke up this morning with my iPhone 5 (not an S model just iphone 5 32 gig) off and burning hot. It overheated badly and I don't even want to turn it on to see if it works. It was to a point that the two camera lenses had sweat marks inside and when I took out the sim it was wet. Yesterday evening I updated to ios 8.0.2. Not going to point fingers but that's a pretty **** big coincidence.

I always keep my GPS location off, find my iphone disabled, bluetooth off, the only thing that was on last night was maybe wifi and cell reception. It was plugged in over night. Genuis appt next so well see what they say.