Line Pressure and Plumbed-In Pre-Infusion

"Line pressure" is the pressure of the water supply feeding the machine. A few makers use it as the soft start, so no pump push is needed at first.

What La Marzocco says

La Marzocco describes pre-infusion as the continuous introduction of water at a low pressure, giving "3 bars or line pressure" as examples.¹ It adds that on its machines the feature is activated by opening a valve, which allows a continuous flow of water at line pressure to saturate the puck. After that the pump fully engages.¹

Note the "for example". Three bars is an example in that description, not a rule for every machine.

What ECM says about plumbing in

The ECM Estetika manual treats a plumbed-in machine and a tank-fed one differently. It recommends active pre-infusion when you use the reservoir. For a plumbed-in machine it recommends passive pre-infusion alone, since line pressure is enough to fully saturate the coffee bed.²

The manual's reason is that pressure from the tank alone isn't enough to evenly saturate the coffee bed, while line pressure is enough.²

Tank or line: what changes

Put the two sources together and a pattern shows. La Marzocco's valve method uses line pressure for the soft start.¹ ECM says line pressure alone is enough for its plumbed-in mode, but with the reservoir it recommends active pre-infusion.²

That's two makers, two machines. It doesn't prove every plumbed-in machine behaves this way. It's a good reason to look up your own.

Both rows come from one manual.²

Reading your own manual

Whether your machine can be plumbed in at all depends on the model. If it can, the manual tells you how to switch from the tank to the line and what the soft start does in each mode.

For the water connection, follow your own product's manual and setup guide.

Two cautions

First, "line pressure" isn't a fixed number. La Marzocco's own example pairs it with 3 bars as one possible low pressure, not as a promise about your supply.¹ Your home's pressure is whatever it is, and the manual is where the maker states what its machine accepts.

Second, not every machine can use the water line for this. Only the machines whose makers describe the feature do. If your manual doesn't mention a valve or a plumbed-in mode, the soft start on your machine works another way, such as the pump pause on the pump machines page.

Where to go next

For the pump-based versions, read how pump machines pre-infuse. For time settings, see settings in the manuals.