I am having a similar issue. My Xenon furnace is 10 years old. We had someone come out and clean/tune it up this year and he 'discovered' that our two stage furnace was running in one stage, so he supposedly set it back to two stage. Since then, our furnace is having startup issues. Blower will start. I will then hear the flames kick in, but it doesn't sound very strong. After about 10 seconds, the flames go out. Blower will continue to blow and the cycle repeats until it eventually starts correctly or shuts down completely. Second repairman and company have replaced circuit board, pressure switch and thermostat. Still same problem. Any ideas? Guy coming back out to the house on Friday and I'm NOT paying for anymore repairs! Furnace is still set to run in two stages.