The PCB may not be 'aware' that the machine is empty. This is usually due to a pressure switch / water metering fault. The PCB could also be to blame.
Do not buy a PCB on a trial and error basis; click repairs@ for an engineer in your area. It will be quicker and cheaper in the long run. If you have tried everything suggested, you have exhausted all the possibilities open to you short of a strip down of the machine.
These machines have numerous issues with their control systems; most are inexpensive to fix and a trained eye will locate the fault easily. The PCB is very expensive and absolutely pointless if it doesn't cure the fault.