The diagram shows the water tank at the rear. The Pump (20) draws water from the tank and it output is connected to the Over Pressure Valve (24). This valve limits the output from the pump of around 15 bar to about 10bar which is preferred for coffee extraction. The “overflow” from the OPV runs back to the tank/pump inlet via hose 27.
The high pressure outlet of the OPV is connected to tee (10) and either fills the boiler via the fill solenoid (8), or if the fill solenoid is closed, passes through the boiler via a tube (indicated in red). Here it picks up heat from the boiler raising the temperature of the water from ambient to around 95C where it reaches the brewhead via pipe 11.
At the brew head is a second solenoid (not numbered). This controls whether the region above the coffee puck receives water from pipe 11, or whether this region is vented to the drip tray via pipes 6 and 7.
The hot water tap connects to the bottom of the boiler via pipe 17.
The steam outlet of the boiler connects to the steam tap via pipe 16, to the boiler pressure gauge (2) , to anti-vaccum valve (13) and boiler pressure switch (15). The pressure switch is set to about 1.5bar.
On top of the boiler is a safety valve, which opens at about 1.8bar and runs to the drip tray via hose 5.