My Carrier WeatherMaker 9200 stopped heating with a code 31. From reading the forum and manuals it looks like it could be one of several things. Blocked drainageBlocked air ductPressure Switch FailureInducer MotorThe motor spins when the system attempts to fire up. I never see a glow in the burner view port. I have been unable to locate the inlet from the manual which shows where to pour antifreeze went winterizing. I read that you could pour water through to see if the drain is clogged. When this first happened, it was off for a day, then came back on by itself. For that reason, I was led to believe it was the drainage. Perhaps the Pressure Switch is getting flaky. Is there a way to test the switch? Or should I simply replace it and work from there? dgp