When a retractable reel has had its hose fully pulled out (past the end of hose marker), then it can lock. This will stop the reel from retracting. While this sounds very basic, there's only one thing to try - grab the hose and give a few short, sharp tugs, be forceful, like starting a lawn mower.

To lock your hose in place when in use

• Standing  close to the mouth of the reel .
•  with a short, sharp 'tug' pull the hose across the face of the unit to lock the hose in place, a sharp tug will release it again.

Caution: Ensure that you do this close to the hose case, and not from out in the garden  
 
If there's been any noise (bangs or cracks?) made by the reel either before, or during you trying to retract it may be an indication that something is broken in the reel - use caution when attempting the short sharp tugs because if the retraction 'takes off' you may find the hose moving very quickly back into the reel.  

Article verified: 1110H, 1120H, 1130H, CH1120, CH1130, CD1120C, 1125H, 1215H, 1225H