iPhone 5s connection priority (Wi-Fi / 4G) My iPhone 5s always (since I bought it 14 months ago) connected to my Wi-Fi at home in priority over the 3G or 4G connection. Recently (for about 2 weeks now) it gives preference to 4G for some reason and my mobile internet service limit (200 MB) goes over in a few minutes if I'm watching a video, for example.

Why would this happen?

I don't remember changing anything in the definitions/options, only thing I did was an update to a new version of iOS, but then it only started to happen about 3 weeks after I did that update, so it seems like it's not related with that.

Can I do anything to stop this from happening?

Is it possible that I'm getting cuts in my wifi service and while the phone does not get connection with the Wi-Fi it starts to get it from the 4G connection without asking or even letting me know?
You should check on the WiFi Assist feature of iOS 9 here. It's on by default, and many have complained about it.


  Turn Wi-Fi Assist on or off
  
  Wi-Fi Assist is on by default. If you don't want your iOS device to
  stay connected to the Internet when you have a poor Wi-Fi connection,
  you can disable Wi-Fi Assist. Go to Settings > Cellular. Then scroll
  down and tap Wi-Fi Assist.