How can I fix my flickmixer as/nz s 3718 model LN21009?

It is most likely to be a sticky valve. I have had the same problem with the exact same model.

You can remove the valve from the tap and but a new one from the hardware store.

Typically, the top of the tap is held on with an screw that requires an allen key. Loosen this and remove the top of the tap. After that you should be able to remove the assembly holding the valve in place using a tap spanner set. You can pick up a set for less than $10. Pull the old valve out and replace it with the new one.

Graeme F
June 2012