Diminished output is usually a sign that the heat exchanger is beginning to clog.
If the machine starts to clog, sometimes the it can be broken free by cleaning the machine using distilled water or, for the Model 1600, compressed air. Both of these methods are outlined in the owner's manual that accompanied the machine. The machine should then be turned on and haze produced. When there is no more haze coming out of the machine, it can be turned off. After every operation, only after the machine has cooled, it should be wiped with a clean damp cloth or paper towel.