If you updated your iPhone to iOS 9, turn this feature off immediately to avoid a ridiculously high bill! There’s a new feature called Wi-Fi Assist that turns off your phones wi-fi when it detects a weak signal strength and switches to cellular data. We normally have 3 bars in the house and weren’t able to connect to our home wi-fi all day until we figured this out.
Go to…Settings -> Cellular -> Scroll to the bottom -> Turn off Wi-Fi Assist
This doesn’t affect customers with unlimited cellular data plans.