Inspect the filter screen where the supply line connects. Remove any debris or deposits that may have built up using a toothbrush or warm running water. If you cannot clear the clog, it will be necessary to replace the valve (the filter is not removable on most inlet valves).
Test the water inlet valve for continuity using a multitester. Set the multitester to the ohms setting X100 (if available, otherwise use the nearest ohm setting). Place a probe on each terminal. The multitester should display a reading of 200 to 500 ohms. If the water inlet valve does not pass this test, it should be replaced. If the inlet valve has two coils, test the second coil in the same way.