The heater micro switch is on the water heating housing where the wires attach to the heater, but i have never known one to go faulty or stick. The switch is activated by the water pressure out put from the pump. The usual problems are a blockage in the clear corrugated hose that runs from the pressure chamber left of machine to the sump center , also the pressure chamber itself, causing low water level, or the heater relay on the pcb in control unit burnt out.
Kenjo, December 2013
