When a shot is made, water escapes the grouphead and runs down the portafilter. What is the most likely problem, if the portafilter is tightly in the grouphead?

When water escapes the grouphead and runs down the portafilter, despite the portafilter being tightly secured, this typically indicates an issue with the group seals. The group seals are responsible for creating a tight seal between the grouphead and the portafilter. If these seals are worn or damaged, they will fail to hold back the water, leading to leakage when a shot is pulled.

A properly functioning machine should prevent water from escaping in this manner. If the seals are not allowing for a proper fit, the pressurized water will find an alternative path and escape. Therefore, the most likely problem in this scenario is worn group seals that require replacement to ensure a proper seal and prevent water from leaking during the espresso extraction process.

Other factors, while they can impact the espresso-making process, do not directly relate to water escaping the portafilter in this context. For instance, the fineness of the coffee grounds, descaling needs, or water temperature issues would not necessarily lead to leakage at the connection point between the grouphead and the portafilter. Instead, they might affect extraction quality or flow rate, but not directly cause water to escape.