Descaling solution can create foam, and foam is air. Air bubbles trigger the flow meter. Run 3–4 tanks of plain water through the machine. If it persists, use the "water booster" method (Step 5).
For the XP series (pump espresso machines), Error 09 usually means the water tank is empty or the steam knob is in the wrong position. Check that the steam knob is fully closed. krups error code 09
Scaling can mimic Error Code 09. Run a manual descaling cycle: Descaling solution can create foam, and foam is air
In older Krups espresso machines (with a digital screen), the code "09" may appear literally on the display. Descaling solution can create foam