My Raicho runs one particular zone -9 with every one that I have setup (1-10). So basically zone 9 keeps running when zone 1 through 10 are running . Even when I disconnect all the zone wire zone 9 still runs. Only when I disconnect the MV then only it does not run. Any idea where the problem is ?
The diaphragm in the valve of zone 9 is likely bad. The pressure drop seen at the valve when another zone on the line turns on can cause the zone to activate. If you can, find what make/model of valve you have, and buy a new, complete valve. Take apart and use as many of the parts (diaphragm, and plastic parts, and top/bonnet from the new valve to rebuild the existing.
The only other thought is some sort of wiring short tied to the MV.
To check this, you can try to manually run one of the zones by turning a bleed screw on the valve itself (try to do quickly to simulate the solenoid opening the valve). If it is the diaphragm, then this will cause zone 9 to run.