Below are photo instructions for cleaning the 3-way solenoid valve in a Rancilio Silvia. This is useful if the release valve isn't releasing water into the back of the drip tray or if you aren't getting any water flow through the group head but you are through the steam wand.
Tools required:
Phillips screwdriver
3mm allen wrench
Once cleaned reinstall the 3-way valve in reverse order and test for flow through the group.