Thanks for the reply. Just some points to remember for anyone searching these topics in future:
1) Going up or down that first time hardly moves the power head, (remember, my system was fully drained since I removed evertything to fit to another power head), just go up and just do it for about 10s after the power head stops moving up if at all.
2) There is a manual release valve on the side of some PTT units, on mine it is the only hex screw (there are 3 others and they all take allan keys, leave these alone)
3) After going up as far as is possible, loosen this manual release valve a full turn and let the power head go all the way down.
4) Now open the fill screw to let some air out and re-fill the cylinder.
5) Repeat about 3 or 4 times, it should go all the way up after at least the third time.