Wi-Fi unstable, sometimes grey, sometimes no networks

Hi,

I have an iPhone 4S with some very strange wi-fi behavior.

The phone sometimes has the known problem of greyed out wifi, but after the next reboot it'll suddenly enable the wifi switch. Although it is enabled it won't find any networks, then all of a sudden it does actually find and connect to networks... It's very hard for me to conclude what the actual issue is here. I've tried everything concerning rebooting/resetting.

It seems to have a lot of trouble with everything connected with the wifi... even opening the wifi menu in the settings sometimes takes ages even though it works sometimes.

Can anyone advise me on my next steps other than heating or freezing the phone which has proven to be a temporary solution in most cases..

Thanks in advance!