S3 good wifi signal but no internet

[AC Question]

My samsung S3 (GT-i9300) can connect with a good signal to my wireless router but I can't connect to internet. It's like no data is being transmitted. The thing is when the phone is very close (less than 2 meters) to the router and no wall between them, everything works fine. If I move further, speed begins to drop, all the way to zero when far enough. As I've said, wifi signal is still good. Other devices and PCs in the house connect with no problem all over the house. I'm also having trouble to even connect to some public wifi (fair/good signal, correct password, won't connect).

I'm now using CM11 m10 with boeffla kernel. I first noticed the problem on CM11 m9. I use wifi infrequently, so I'm not absolutely sure when this problem started. But I can confirm that it worked perfectly when the phone was on android 4.1.2 (stock samsung) and CM11 m4 a while back. I did data, cache and dalvik cache wipe everytime before flashing.

Could this be a hardware problem? I want to be sure before sending it in for repairs.

What I've tried to fix this:
-Flashing latest stock samsung rom for my country (4.3), the last 4.1.2 stock samsung rom, reflashing cm11 m10 twice (after factory reset and full wipe)
-Toggling and tweaking every wifi settings on the phone (as far as I know)
-Using static IP on phone
-The usual phone and router reboot
-'Forgetting' the network and reconnecting
-Changed router to TKIP only, AES only, and auto
-Changed to open unsecured connection
-Changed wireless channel
-Changed wireless mode (n/g/b) and bandwidth(20/40mhz)
-Tried 'fixer' apps (wifi fixer etc.)
-Changing phone kernel (from cm to boeffla)

 

[B. Diddy]

Welcome to Android Central! Is your phone's Bluetooth on? There can sometimes be interference, so try turning Bluetooth off. While you're at it, also turn off mobile data. Now see if the connection is better.

 

[gasher3]

Hi I'm the original poster. Thanks but that doesn't seem to be the problem or solution. Bluetooth was always off, I toggled it on then off just to be sure and also turned off mobile data, still the same result.

 

[B. Diddy]

Another thought--if on the off chance there's a loose physical connection for the wi-fi antenna, see what happens if you squeeze the phone in various ways, in case that improves the connection and therefore the reception. It's a longshot, but won't hurt to try.