I had a kolsch I boiled and pitched a Wyeast 2575 and never saw one single bubble in my air lock. I left in my fermenter at 64 degrees for a month just to be doing it. I pulled it out and tested the gravity and it had fallen from 1.049 to 1.016. I left it for another week and got the FG down to 1.014. So, that's five full weeks of fermenting and the air lock never saw any action. I've been lagering this one for about a month now and it's almost ready for kegging.
The only difference in my story and yours is that I did pitch mine with a starter. I don't know if that made the difference or not, but I always pitch with a starter.