What should I do if the espresso only drips or doesn't flow at all?

This indicates over-extraction. The coffee may be ground too finely, there may be too much coffee in the filter basket, or the coffee may be tamped too firmly. Use a slightly coarser grind, lower the dose of coffee, or tamp between 30–40lbs (15–20kg) of pressure. You can also trim the coffee dose using the Razor™ dose trimming tool. (Page 29)