iPhone 6 wont remember to auto connect to my companies wifi

My company recently gave us access to a public WIFI. Its a big corporate company, so access to IT support is a nightmare.

You connect to it in the normal way, but there is a pop up login screen the first time you use it, and you only need to log in once every 30 days - It remembers your details. So I entered the details and I got the "Success" page and Wi-Fi is connected and im going fine.

If I stop using the wifi for a while it cuts me off.

If I go home and come back the next day, its not connected.

But all I have to do to resolve is go to Wifi and click on it and it connects no problem - no need to login or anything.

My issue is that this is happening to both me and my boss (on an iphone6+), but not my other collegues?

They are using both an iphone5 and a iPhone6+, but they remain connected at all times in the building, whether when they leave and return, or if they leave their phones idle.

I have compared the wifi settings and everything is identical.

We are all on the most upto date ios8.3

Any ideas?????

thanks!