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It's June so my furnace has been off for a while. But it's cold today and I have a sick kid home so I tried to start my furnace but it's not working. I'm getting an LED code with three red flashes which, according to the label on the inside of the access cover, means "Vent intake or termination problem". I noticed that the filter (16 x 20 x 1) was out of place and kind of pulled a little into the unit. But it didn't look like it damaged anything. It was also really dirty, so I figured maybe the issue was that the dirty filter blocked the air enough that it triggered the error. So I bought a new filter and replaced it.

I couldn't find a "lockout reset" button on the unit so I reset the LED fault indicator and turned the unit off for a minute or so, hoping that would reset it. That didn't work and I'm still getting the 3 red flashes. I waited an hour, thinking that it might reset automatically (which I know is the case with some units) but that didn't work either.

Any suggestions as to what else I can check? The intake where the filter goes looks fine; as for the outgoing vent--I don't see how I can check that for a blockage. It vents through a metal vent into the chimney. I also don't understand how that would have gotten blocked up.

The unit is a York TG8S gas furnace. I haven't been able to find a service manual online--just a "technical document" that wasn't much help and an owner's manual that was pretty useless from a technical point of view.

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    The vent usually refers to the induction system (the exhaust fan). Check for blockage outside, where the PVC pipe terminates. There may also be a problem with the inducer fan itself. I've had to replace them when they get weak. Sometimes the pressure sensor fails or the sensor vacuum tube gets plugged with water deposits, insect material, etc. – isherwood Jun 5 '18 at 19:06
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    By the way, blockage may not be immediately apparent. It's only by the grace of Zeus that I heard my then-toddler son dropping landscape rock into my exhaust pipe. I had to shop-vac them out. If I hadn't heard it happen I'd have probably paid a technician to come and scratch his head for a while. – isherwood Jun 5 '18 at 20:00
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Thank you so much for having this thread. My wife woke me up at 4 in the morning, and told me that the furnace wasn't working. Last year my son put hot wheels cars in the vent and they made it all the way down to the exhaust fan and damaged the fins a bit, but it still worked. My fear was that the fan had finally gone out according to your information. I went through all the air lines to sensors, and such and discovered small amounts of debris and water in each of the lines. Once they were cleaned/ drained she fired right up! Sincerely, a warm home owner in North Dakota.

  • Welcome to Home Improvement! Please don't add "thanks" as answers. Invest some time in the site and you will gain sufficient privileges to upvote answers you like, which is the Home Improvement way of saying thank you. – Daniel Griscom Oct 21 '18 at 11:02
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Just an update on, and solution to, this question, which I forgot about until Michael's answer yesterday. A couple of weeks ago, I had an HVAC tech friend of mine take a look and, as isherwood suggested, it was the inductor motor. It was trying to start but wouldn't. Turns out it was jammed up with a bird. A bird must have gotten into the intake and got sucked into the inductor motor, which then seized up. The motor was taken out, bird was removed, and motor was re-installed and now everything is working again.

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