The pressure switch on the heater will be to make sure water is present inside the heater tube before turning the heater on. For safety reasons you do not want the heater on with no water flowing. The heater is not switched on for the drying. It uses the heat from the heating of the final rinse water to dry the dishes, that is why drying is poor and takes a long time on Baumatic dishwashers. You buy cheap dishwashers you get cheap poor performance unfortunately. Google Baumatic dishwashers and read the poor reviews.
George
June 2017