I have a Toro ( sorry... don't have the model number at the moment ) sprinkler control system with rain sensor. My yard is divided into 5 Zones. All 5 zones run fine ( 15 and 20 min intervals ) but Zone one constantly runs with all the other 4 zones. I don't know how long this has been happening as I leave for work just after Zone 1 starts. I happened to be home and saw it last Wednesday

What I've done/noted:

1. Zone 5 had a broken sprinkler head, replaced it. Still have Zone 1 issue
2. Looked at the Zone valve boxes ( 2) bone dry, no leaks from any of the valves and all the wiring is fine.

Not sure what to try next.

The system came with the house. I bout it from the original owner

 

Hello and welcome to the forums...

Sounds like that valve is stuck open on zone one. Try to replace the diaphragm.. The reason why it does not run constantly when the sprinkler is off is most likely because you have a master valve that shuts the water off...