Thanks for the reply. Hmm...the question was that my HTC Desire 310 keeps reverting to vibrate only for the phone, even though I have set it to Loudest Ring and vibrate.
I have id'd one repeatable way to make it happen, but I am now watching to see if that's the only reason it does it. I use a VOIP app on the phone, which, rather amusingly can now phone itself, VOIP app to mobile number. I have done this a few times to check the VOIP service. This sets the phone ring tone to the wrong setting: I have no idea why. Having id'd this cause I can deal with that. But I don't recall having done it a couple of times the ringer has changed though, so I am still looking and waiting.