I have 4 devices I connect to by BT regularly. IF I used BT with one of those last, say the Logitech mini boombox, then turning the BT off or on in my control center will work. I only paired it once to put it in my list. And no, no code for it--just push the button until it pings for the original pairing- after that, just turn it on and turn in BT in CC. But--if I want to use my Apple BT keyboard, even though it is paired (and yes, it did require a code being entered to pair it originally and put it in my BT list) and it wasn't the last one being used it doesn't always connect--occasionally I have to open settings, click beside its name to connect. However, all 4 devices are "paired" and only have to be turned on usually, with the occasional having to touch its name in the BT list in settings.
Should say ipad Air, but it worked the same on my Ipad 3 with IOS7.