How to automatically switch from WiFi to mobile data when no internet on WiFi? I have a wifi router at home with adsl connection. But internet connection from our service provider keeps dropping off. Unfortunately, the service provider I am using is much better compared to others.

In my mobile phone (galaxy s3) I have the wifi and mobile data enabled. So when I am at home it automatically gets connected to my home wifi. Switching from mobile data to WiFi works good.

But is it possible to automatically switch to mobile data when there is no internet on the WiFi connection? 

Is there an app which can check if there is a internet connection with the current connection (data or wifi) and do the switching automatically. Let's say for 30 minutes and switch back to wifi and so on? 

I will be happy to even use 2 or more apps to achieve this? Any tips or suggestions are welcome.
If you have 4.4.x you can go to Settings -> Wi-Fi -> press Menu button -> Advanced Wi-Fi -> check Internet available (another possible name -  "Avoid poor connection") . That wil disconnect WiFi automatically when there is no internet in it.