I've been having trouble with my iPhone reading WiFi networks. A couple months ago I got my 4S replaced because of damage but I had a warranty and got a new one. Ever since then it doesn't automatically read wifi networks and is constantly on 4G. Even when i try to manually search for networks it won't work. I tried calling my service provider and they did troubleshooting with me (tried to turn off/on, reset network settings, reset phone) and it still didn't help. They advised me to call Apple. My warranty has since expired.
I tried the basic troubleshooting and it won't work. After the phone restarts the WiFi option to turn off/on is just greyed out and I can't even turn wifi on so I have to restart the phone AGAIN. It's really annoying.