I like Nails
Join Date: Nov 2011
Location: Sandhills of NC
Because it is only one zone that has an issue, it sounds like a valve problem. Could be the solenoid is bad, and not allowing the valve to open completely. But usually when the solenoid is bad, the valve remains open partially.
Try manually opening the valve to see if it allows full pressure, if it does, than the valve needs some work. Could be a little grit or dirt in the little hole that allows water to pass, and the valve to open. You can clean that out with a thin wire. Could also need a new diaphragm. Another, less likely issue, could be the clock has a problem and is not sending enough juice to the solenoid to open fully. If you have an unused zone, switch the wires for the problem zone to the unused zone.