Question
I have a 8 zone setup. 8th zone added and was functioning till winter set last year. This year, I find all zones including the new 8th zone that was added functioning well except zone 6. I located the valve and found a knob labelled on/off that can be rotated roughly 90 degrees. If I turn it even 15 degrees from the off position the heads spay water.  However the controller does not seem to automatically turn on the zone. I have reset the knob to the off position as it is in the other zones' valves.

Expert's advice is sincerely appreciated.

Karl

Answer
The knob is a manual bleed that turns on the valve without a signal from the controller.  It is more likely you have an electrical problem,  Make sure the wire connections at the valve are good, try replacing them.  If you know how to use a multimeter, check for 24 Volts at the valve and at the controller station.  If the wires are good and it still doesnt work, try replacing the solenoid.