Help please!....... Voltage too low to turn the motor!

Hi, My motor isn't getting enough voltage to turn properly. Should be 18 volts only getting 13.2 at the lnb.
The Openbox V8S is kicking out 13.40 volts.
The Openbox has in the menu an option for voltage on or off, but I can't see an option for upping the voltage.

Help!

Thanks for the info.
The manual is next to useless.

Well that narrows the problem down to the motor.

Cheers