My RainBird timer has four zones. Zones 1,2 and 4 are great. Zone 3 flashes "ERR" with no explanation. There's nothing in the manual about it. Any have a clue about this?
Chances are that your #3 solenoid is shorted out. You could disconnect the solenoid from the field wiring at the valve and try to turn #3 on from the controller. If you don't get an error message, replace the solenoid.
Texas Licensed Irrigator #1897 since 1984
If zone says error that is a bad solenoid. Read about it at http://www.actionirrigation.com/Troubleshoot_sprinklers.html
Here is a link that might be useful: sprinkler help desk