Skimmer stopped producing bubbles.

[jslmk4]

Hi All, I have a Eshopps S-120 skimmer in my sump for the past 8 months. A few days ago I noticed it stopped producing micro bubbles so I cleaned it thoroughly and put it back and it worked fine. 3 days later the same thing happened so I rinsed it in freshwater again and cleaned the air line and venturi. Again it worked fine for 3 days, then no bubbles. So now it sits in my sump full of water with no micro bubbles. Any help would be appreciated. Thanks......... John