Hi! I had the same issue with my iPhone 4S. It was updated to iOS 9, but now unable to check for updates. somewhere it has been mentioned that you may use another wi-fi for checking updates. I hope it will work. Another way is to update using iTunes in your pc or mac. My mac has detected the update and i am planning to update using iTunes. 8.8.8.8 didn't work for my iPhone. also the reset the iPhone to update the phone is pointless as you will always need to reset iPhone as and when the updates are available. There must be some solution. For time being best way is to update using iTunes in your pc or mac.