I have had 2 high efficiency Carrier systems. When they run they are great. But I had the same problem with my second one. I believe they ended up replacing the limit switch and the inducer motor. Apparently the unit was tripping off after it would fail repeatedly to start. It was determined - if my memory serves me correctly - that the system thought there was a back pressure condition which prevented proper venting. Their action, to the best of my knowledge, corrected the problem.