One Sprinkler in One Zone wont stop

[philipsb]

I have a funny situation, all of my zones used to work well but now in one zone when the timer shuts it down all the sprinkler heads shut down but one. This sprinkler head will not stop watering, I shutdown the power, unplugged the unit still wont stop. I then stopped at the main water line then it stopped, I restart the water at the main line and it is then fine. Next time the zone starts the story repeats.

Can anyone advice me on the problem here?
If it is a faulty solenoid/valve then all the sprinklers in that zone should get the water and all of them should be watering but accept this one head all of them turn off correctly!
If the problem is with the sprinkler then where is the water coming from?

This problem is driving me nuts....any help is appreciated.

Thanks!

[tomm]

More than likely a faulty valve diaphragm.

[Gary Swart]

The problem has to be at the zone valve. It is just not closing completely until there is not water pressure against it. As suggest, it may be a faulty or dirty diaphragm. I have had the same problem in the past and ended up replacing and upgrading all of the valves in my system as a preventive measure. They were approximately 20 years old at the time, so I figured they had earned retirement.

[philipsb]

In that case I will go ahead and replace the valve and see. Thanks for the help!

[tomm]

Let us know the make and model of valve and/or post a picture!