Check valve (non-return valve)

A one-way valve that allows water to flow in one direction only. Used throughout an espresso machine — in the pump output, the steam line, and the water inlet — to prevent backflow.

Why it matters — Check valves stop hot water from siphoning backward into cold lines, prevent steam from contaminating the brew path, and protect components from water hammer. A failed check valve usually shows up as flow problems or unexpected pressure behaviour.

Good to know

• Check valves are mechanical and can be cleaned; some are replaceable as a whole unit.
• Symptoms of a failed check valve include: water dripping from the wand when not in use, pressure not building correctly, or unusual gurgling sounds during operation.