Unstable WiFi (err_name_not_resolved)

I have the newest fw for my S5 and I have a lot of problems with WiFi. Sometimes I just get the err_name_not_resolved
In chrome and then I have to disable and enable WiFi and everything is OK again for perhaps an hour or a day... My phone also keeps getting warm and I suspect it has something to do with WiFi?!

I have tried reinstall my phone and my router is a Asus new one.

Please help. I had problems with WiFi since galaxy s3... (On different routers)