The water level sensor is electronic & part of the main controller PCB. If it is faulty then you will have to replace the main controller. The only thing you can try is open the top panel. Pull the air tube off the controller on the right hand side. Blow down the air tube to make sure it is clear. There may be a small blockage causing it to play up. If that does not fix it then you will have to call someone in to replace the PCB.
Lincoln Appliance NZ, April 2010