I just moved into a new house two months ago. The house was built in 2006. For the first month the furnace worked just fine. About a month ago I turned the thermostat down because we were going to be leaving for the day. When we came home I turned the thermostat back up and the furnace would not light. The furnace (Bryant 90) was blinking a code of 31. Code 31 is a pressure switch related issue. The furnace turns on for about 90 seconds (blower motor I beleive) then that turns off and the inducer motor comes on. That stays on for about five seconds and that's when the code starts blinking. A cousin of mine who knows about furnaces came over and he cleaned it all up pretty good but it didn't fix the problem. He played with the pressure switch and loosened it with an alan wrench. We made sure the switch still functioned by plugging up the vent on the roof to see if the furnace would shut itself off, and it did when the vent was about three quarters blocked. My cousin talked to his bosses and they told him to clean a few different hoses and to retighten the pressure switch. He also checked the amps to the inducer motor which was normal he said. When he retightened the switch it went back to blinking a 31 code. When he loosened the switch again it started working. We bought a new pressure switch thinking that would fix the problem but it didn't. We put the old pressure switch back on only to find we had to loosen the switch further to make the furnace work. It has been working fine for the last three days now but I would really like to get it fixed with a good (not tampered with) switch. We have kind of run out of ideas.
you can't adjust those!!!!!!! They come from the factory preset to a specified pressure. When using the allen wrench that is what you are doing (adjusting the pressure) there by changing the pressure it closes at! GET SOMEONE OUT THERE WHO KNOWS WHAT THEY ARE DOING! 99% of the time it is not the press switch! check the intake under the burners to see if there is something stuck in the screen. Also check the intake and exhaust for blockages.