Delonghi two shot button only dispenses water for one shot

Delonghi two shot button only dispenses water for one shot

Over the last couple of days, my Delonghi EC680.BK has suddenly begun only dispensing enough water for one shot although I press the two shot button. This happens, even when the sump assembly is not attached. The machine has been descaled and is clean/not blocked and the water tank is correctly fitted.