If the water level sensor insulator (-A) is covered with
impurities, it may signal that the water level is high in the
steam generation tank, even though it may actually be low.
 
Also, if there are impurities on the water level sensor body,
it may signal that the water level is low, even though the
water level is normal.
 
Remove the wire from the wire connection terminal (-C).
Wipe the water sensor insulator and body clean with a wet cloth.
If the sensor is bent as shown in the picture, it will not function
  properly and water will not be supplied. Straighten and reposition
  using Teflon tape, and reassemble.