First of all, this is a good reference thread...lots of good trouble shooting options.
This "no sound" problem was going on for about a week on my iPad Air. I finally started trouble shooting it today.
I had the same problem as many others here...no sound from speakers, but did have sound from headphones.
I switch off between Bose wired headphones and a pair of Logitech bluetooth headphones. All of a sudden no sound when not using the headphones.
After trying the reboots, dusty charge slot, etc, I went into settings/bluetooth and first disconnected all the bluetooth devices and then played music from iTunes to test...No sound. I turned bluetooth off, tada!, Sound!
Just seemed like Bluetooth got hung-up blocking sound to speakers.
iPad sound works great again!