Had a very similar problem with the digital one today, it took me ages to figure out what was wrong.
I found I had a stoplock Hozelock connector on the reel centre, when I stopped the flow it pressurised, and the connector pushed back, the stoplock then came into operation and stopped the water going to the reel.
I took the stoplock out of the connector and it worked fine.
check your water flow before it goes into the hose reel, or just look into the connector to make sure it's not fitted with a stop.