Water running through with no resistance, and a thin watery shot, has a short list of causes.
Start with the coffee
Grind too coarse. By far the most common. The bed offers no resistance, water runs straight through, and the gauge never rises.
Dose too low. Not enough coffee to fill the basket properly.
Pressurised basket used with fine coffee, or a non-pressurised basket used with supermarket pre-ground. Check which type you have.
Test without coffee
Insert a blind basket — no holes — and run the pump. The gauge should reach the machine’s maximum, usually 9 to 12 bar.
Pressure builds normally — the problem is the coffee or the grind. Pressure stays low — the problem is the machine.
Machine causes
The pump is not primed. Air in the line. Run water through the steam wand or hot water tap until it flows steadily.
The water tank is not seated, or its valve is not opening.
A blocked inlet filter or screen. Scale or coffee fines.
Scale in the lines. Descale.
A failed OPV — overpressure valve — dumping to the tank continuously.
A worn or failing pump. Vibration pumps last years and do eventually fail.
The order
Grind finer first. It costs nothing and it is usually the answer.
Last reviewed 8 August 2026