7 year old Heil furnace, started blowing cold air yesterday and the status LED is doing 3 blinks which means "pressure switch open when should be closed". I removed the tube off the switch and used a straw to suck/blow a few times very gently and heard the switch engaging normally. I then blew into the tube itself and reconnected and it works immediately. Briefly (20-30 min). Then cold air again. I blow into the tube again (didn't touch the pressure switch again), and it works again. Briefly. Repeat. Are we thinking this is crud somewhere blocking the airflow from the tube and I'm dislodging it temporarily when I blow into the tube? Or does this sound like a bad pressure switch? Thanks.

Hi, First, I let my filter stay dirty for too long. The furnace was running, but no heat was coming out. So I changed the filter. But nothing. I cleaned the limit switch with a cloth because I read the 4 blinking lights indicated something was wrong with it, but that didn't help. I turned the furnace back on, but, like always, the flames light up, theres the normal hum like it's about to start blowing air, but no hot air is being forcibly pushed out via the loud fan. I can only hear small sound with hot air barely seeping through my vents. Just checked, while keeping the door switched depressed, I fired up the heat and the blower fan(?) won't spin, even though while the flames ignite and everything. Could the blower fan be the problem? Or is the the limit switch (indicated by the blinking 4 times) [I]causing [I]the fan not to spin? Like, do you think I have to get a new limit switch and test that first. How do I determine what the issue is? Or should I just call someone to fix it, and how much am I looking at? I'm just in a serious bind because it's 5 degress, and I have two kids in the house. Although they have a heater in their room, and spend the day at school, it's quite cold in here. Thanks for you help in advance! [/I][/I]