This usually happens when there are particles blocking
the water supply solenoid(-B). Turn off the power, and
disassemble and clean following these instructions.
 
Unscrew the coil bolt (-A).
Lift up and remove the coil (-B).
  (It is unnecessary to disconnect the wires.)
Unscrew the 4 sheet cover bolts (-C) using a wrench.
Lay the sheet cover (-D) flat and remove, taking care not to
  let any internal parts fall out.
Remove any foreign particle in the internal water hole (-E),
  and reassemble by following the above instructions in
  reverse.
 
NOTICE : When putting the sheet cover (-D) back on,
  make sure that the internal gasket (circular
  packing) is in its original position before putting it
  back together.