I don't know anything about that particular system, but I can offer a few things to check.
If your system is using an air pump to deliver the product, and is dead headed until a delivery solenoid opens, verify that the coil of the delivery solenoid has power. If the coil is energized, and the pump doesn't kick on, then the solenoid is noy opening. If this is the case, and you are using Dema, or Kip solenoids, they are prone to swelling, and either sticking in the closed position, or sometimes, even in the open position. If you are using the Kip solenoids, I know that there are replacement plungers available, and there is a viton option on those. I would expect that there are replacement plungers for the Dema as well.
I would venture a guess that the plungers have swollen, and this is what is causing your issue, especially since you said you recently changed pre soak. ( sometimes different soaps don't like to play together.)
If you are injecting air into your presoak
soap,( in the equipment room, or in a manifold in the bay), make sure your air pressure is not turned up too high, so that it stops the flow of
soap.
The other thing to check for, is whether the check valve is plugged, and not allowing the
soap to get by.
HTH