Possible cause:
Inadequate rinsing after descaling.
Rinse as specified in this step-by-step guide:
Failure to clean as described in this guide invalidates the guarantee.
Obtain descaler solution by dilating the descaler with water, following the instructions on the pack.
The ON light comes on.
At intervals, turn the steam dial to deliver water from the cappuccino maker. Then, interrupt the water delivery by pressing the express coffee/hot water button button and leave the solution to work for about 5 minutes.
Repeat this another 3 times until the tank is empty.
Put back in the coffee machine.
Deliver water until the tank is empty.
Put back into the coffee machine.
Deliver water until the tank is empty.