1) Disable Wi-Fi networking service
Many iOS 8 users said that they fixed their Wi-Fi issues by disabling Wi-Fi networking service, you can give it a try by going to Settings > Privacy > Location Services > System Services. This only relates to your location being used for Wi-Fi Networking, so it doesn’t disable Wi-Fi entirely.
2) Reset network settings
If the above solution didn’t work with you, better to try reseting your Wi-Fi network settings.. Almost all networking related issues I’ve experienced have been fixed after resetting network settings.
Here’s how to reset it: To reset network settings, open the Settings app and navigate to Settings > General > Reset and tap on Reset Network Settings.
3) Set a custom DNS
Often times, if your ISPs DNS servers are having problems, you can switch to Google DNS or OpenDNS. You can follow the instructions in the post linked below to change your DNS settings.
4) Make a full restore and setup as a new iPhone
Now if all of the above tips didn’t work with you, we recommend you to make a quick restore for your device and setup it as a new iPhone, maybe restoring will fix this problem..
Let us know in the comments if you faced any Wi-Fi issues, and if so, were you able to fix the issues with these tips.