My new house has a 6 month old Goodman 92% HE furnace. A couple of days ago, it began cycling in an odd way. It would begin with the normal warmup phase (whatever that is), go to the next stage where it's actually blowing heat through the ducts, but afterward, the smaller warmup motor would continue running for between 5 and 20 minutes. Other times, the warmup stage would go on for 15 minutes BEFORE heat began blowing, and sometimes it would never reach the true heating stage.
By the way, when I say "warmup phase", I don't mean there's a flame yet. I'm referring (perhaps incorrectly) to the stage where the thing is checking for proper ventilation or whatever it's doing.
ANYWAY.....my neighbor's car alarm went off at 3:30 AM (the tenth time since this morning), and since nobody in my house is up watching TV, it's very quiet. The furnace began doing it's odd thing again, so I went down in the basement to curse at it. Because the house is quiet, I heard something interesting. Standing right under the PVC vent pipe, I heard what sounded like water - about as much as you'd hear if you were in the basement as the last 3 seconds of water drained out of the bath tub. "WTF?", I said to myself. I looked up and noticed that the installer had nailed a pipe hanger in such a way that the thing had come loose, leaving the 15 ft span of PVC with a downward bow in the middle. I went upstairs, had a few pieces of fresh pineapple, went down to the cellar again, pushed up on the pipe to straighten it, heard water head toward the outside, and voila! The furnace has cycled normally 5 times so far.
Was collected moisture in the pipe preventing the furnace from being satisfied with the venting?
Or was the pineapple a factor? On the next episode of Nova.....fruit and appliances....what science doesn't know yet.