For the past few months I have poor flow from my KWC kitchen faucet sprayer. It does not matter whether I want the "spray" or the regular flow. It's very erratic; sometimes it's bareable and sometimes its less than a trickle.

The Problem is NOT the aerator, I have removed that and cleaned it out.

The folks at KWC are less than helpful, suggesting that I could remove the backflow preventor in the base of the handle (but I cannot do that) or buy a new handle ($110.00 for a piece of plastic junk!).

Any suggestions?

Try this. Unscrew the sprayer head, )(see image). Now with the sprayer head removed turn the water back on. You should have a strong stream coming out of the open hose. If not, click on back and tell me about it.
If the stream's strong soak the sprayer head in bleach overnight. Reassemble and test. Good luck, Tom

Hanistor: I am sorry but Tom is not showing the Swiss made KWC pull out sprayer. I think Mr. Karrer is turning in grave... :D

It is most likely the handle itself. I hate to say it, but if that's the case the best way to restore your flow is to replace the handle.

But before you do that you can check on few obvious things: Unscrew the handle from the hose and run water through the hose only. See how much flow/pressure you get. If you get good flow, you know it is the handle. If you still get small flow, then replace the hose.

It could also be the back flow preventer that is between hose and faucet. Dirt accumulates inside and eventually blocks the flow.

KWC faucet are very delicate faucets. Unless you have some kind of filter on your water system this type of faucets will clog again. And yes, KWC is a high-end faucet and genuine parts are very expensive. And from my own experience, I must agree with you: KWC people are not (... and have never been... ) the most helpful people...