happens far too often. Especially with cheap valves or dirty water.

when power is sent to a selenoid valve, the magnetic power pulls open the valve. Water flows through.
when power is cut off, if there is any dirt or trash when the valve closes the trash (and water pressure) will hold open the valve.

on come valves with flow control, you can turn the flow on/off several times to try to flush it.... This rarely works long term.

taking the valve apart and cleaning it works well, as does replacing the valve.

best of luck, and sorry I kinda simplified these processes some :-)

Drew

Check to see if the manual bleed is open on the valve in question. Also check the solenoid itself - turn it clockwise as far as it will go to make sure it is firmly seated.

If the valve in question is a Toro Flo-Pro, do yourself a favor and replace it - they're notorious for failing.