Kinda sounds like a venting issue. You should get a parts breakdown and an installation manual and see if the venting was installed correctly. I did one not to long ago, and the installer didnt install a baffle in the termination....or something lika that.
It made the pilot go out all the time.
Now the freaks are on television, the freaks are in the movies. And its no longer the sideshow, its the whole show. The colorful circus and the clowns and the elephants, for all intents and purposes, are gone, and were dealing only with the freaks. - Jonathan Winters