Hi Erika,
Underneath the boiler you will find a metal flexable hose (silver colour), You wil need a screwdriver to turn on a screw valve to put water back into the system. You will hear the water going through. Before doing this press the bottom left hand button on the control panel to show the pressure. The manuel will tell you how to do this. Finally do not exceed the pressure of 2.6 or the system will vent itself. If you do this by mistake it's not a problem you will just need to go through the process again. Hope you find this usefull...
bob, November 2007