I couldn't get it to work the other day. Was this because I was trying it at an unlicensed airfield?

I just checked this out in simulator mode on our office ipad, and I can see the ILS kick in at Perranporth... We certainly do have the threshold co-ordinates, and as you are approaching your chosen runway the centre of the HSI should change from a plane outline to a circular outline. The "crosshairs" should then begin to converge.