If the machine behaves as though the tank is empty — refusing to brew, or showing a low-water condition — even with a full tank, the small float switch inside the tank is the most likely cause.
01Check the silicone tubes inside the tank
Per Gaggia's own manual, when reinserting the tank, make sure the silicone tubes are fully inside the tank and correctly positioned — if they've shifted or kinked, the float can't move freely to register the correct water level.
02Float physically stuck or dirty
Mineral deposits or general grime can cause the float itself to stick in the "empty" position even in water. Remove the tank, and if accessible on your model, gently clean the float mechanism with a soft brush and rinse thoroughly.
03Tank not seated correctly
Beyond the float itself, confirm the tank is pushed in fully and seated against the machine body — a tank that's slightly askew can prevent the float's signal from reaching the machine's sensor correctly, even with a functioning float.