I got my solder to melt!
I tried the suggestions of attempting to melt some solder on some off cuts in another room and it worked!
I then went back to my work station and tried (exact same way) and it didn't melt. On closing the blind on the window I'm working right next to, it melted!
So I'm thinking that the window is the problem. I'm still having some trouble when the ring is suspended in a third arm, but maybe if I move my work station this could fix the problem.
Thanks so much for your help everyone.