Somehow/somewhere, there must be a valve/solenoid that directs the flow through either the group or steam/water outlet. *
Or, perhaps this is simply controlled by whether the steam valve is open or not.
Do you get water through the group when the brew switch is on?
The steam pressure is *produced inside boiler and does not require the use of the pump.
But be aware that the *pumping process [water and/or brew] will fill up your boiler, however steaming will depleate it. *
Therefore after steaming, you need to refill the boiler by running the pump....most of us pull a blank shot [empty PF] *following steaming as it fills the boiler, cleans the path and brings the group temp back down. *