My name is Peter. I am a retired field service appliance technician.
There is a solenoid valve on the larger pump.
1.) Unplug your unit.
2.) On the back of the top cover are two screws. Remove them.
3.) Pull the cover back about 1/2" and lift the cover off.
4.) Looking down behind the dispenser you will see several components:
a.) Three black rubber hoses connected to two water valves.
Substitution Part Number 34001210 - Cost: $43.00
You can probably take the hose to your local Home Depot or Lowes and find a match for considerable less, if replacement is needed.
1.) Remove the hose clamps and remove the hose.
2.) Try to blow through the hose - is it blocked?
3.) Can you run a coat hanger through it to clear?
b.) There are two water valves. Disconnect and clean. There is the larger one which has a solenoid valve.
On the bottom of the larger solenoid valve, disconnect the two wire connectors. With a multi-meter (If you do not have one they are only about $25.00, a good investment to check electrical components)
Set the meter on the lowest Ohms. Placing one meter lead on the one connector and the other meter lead on the other connector
you should get a reading of '0'. If not the solenoid is bad.
c.) Ok, lets not forget the sensor;
Part Number 34001209 - Cost: $49.00
This is in the same area. There is no way to check this sensor if it is bad. You replace it only if all of the above is operational components check out ok.