As the modern QCC valve has a check valve builtin to it thus if nothing is connected to valve, even when open nothing will come out of the LPG cylinder valve. Therefore if you have nothing connected to it and the valve has been left on from the last time of use, nothing will come out , you try to turn the valve ON and it wont move! Brain will say "the valve is jammed SHUT", wrong! don't use a stillson wrench to open it, first try to CLOSE the valve. Thus never fully open the valve, if you must, always put a turn back from fully open, then use the cylinder. then the next time you go to open the valve it will move, brain will say "oh bother didn't shut the valve last time."
A bit wordy but hopefully gets the message across.
35ft Fleetwood Bounder since 2008, have also had 2 caravans and Converted Seddon 10.5 mtr Motorhome since 1995ish. Live on the Kapiti Coast.