Is the water reservoir full?
Check the water reservoir may be empty, or the brewing boiler may not be filled.
Is the hose kinked?
Check to make sure the reservoir siphon hose isn't kinked or improperly placed.
Does the screen need to be cleaned?
Check to see if the shower screen is clogged or dirty, it may require cleaning.
Does the machine need to be cleaned?
Espresso Machine may need to be descaled.
Are the correct size grounds being used?
Ensure the coffee isn't too finely ground. Also, check to make sure that the coffee isn't too firmly tamped.