My iPhone 4s with iOS 8 has stopped functioning correctly all of a sudden. It shows searching for network and keeps heating up. I have already tried resetting network settings and have also put it to factory settings but no avail. If I try to search for a carrier manually, it shows "No service" but keeps heating up. If I remove the SIM it just works perfectly fine and there is no issue at all. I am able to use all apps etc perfectly. Any clues on what I can do and if this issue can somehow be corrected?
Perhaps your Carrier Network Settings have been corrupted or altered in some way. In this case, the phone would be searching incorrectly for the carrier towers, or trying to connect and continually getting refused due to a setting error.
Apple provides details on checking and manually editing the settings, but getting them wrong can cause problems like you are experiencing.
You can also restore your phone via iTunes, which will wipe the iPhone, reinstall iOS, and redownload the carrier settings. After confirming the restore worked, you can then restore from a backup to get your apps and settings back.