I had this problem with a Fisher & Paykel. Solenoid was OK but water was only dribbing through. The F&P valves are able to be disembled - 1. Take off solenoid. 2. Unscrew top of valve - its all plastic but with firm pressure from pliers, the top of the valve, where the coil sits, will unscrew from the body. 3. Remove the washer & check for dirt or gunk on the washer or seat. 4. Clean & check for free movement of valve.
If you are unsure if this has corrected the problem try swapping the hot & cold wires over and thereby confirming you have current from the controller.
Last option - Buy a complete new solenoid/valve.
Lloyd H, February 2008