I've replaced hot surface ignitor and pressure switch and no luck. If I remove tube from inducer and draw air from pressure switch, the ignitor begins to glow but not long enough for burners to start. Other times when I've tried this trick, the blower starts but burners do not. I checked the vent pipes on the roof and they don't appear to be obstructed -- was able to stick broom handle in all the way. The other furnace, which serves the ground floor, and is about 25 years old, still runs fine. Assuming both furnaces vent through the same pipe? Condensation pipes are the same. Any help would be much appreciated. Thanks

If there are return air registers on the floor the heat will reach the floor. If no return air registers you will deffinetly have a problem.