Hi, I've got a goodman furnace (mod. # GHT070-3) it's about 5 years old. Recently, the heat will only kick on for about 30 seconds then shut off. It's giving me 4 flashes: Open limit switch, then it kicks off. After that it gives me 3 flashes and turns back on (pressure switch).
It seems the furnance only does this when it is colder and it has to work harder, because when it's only in the 40-50's or so I don't notice the furnace acting up like this.

I pulled the limit switch out and just physically inspected it, I didn't notice any breaks or anything (though I don't know what to look for).
I looked at the back of the circuit board and didn't notice any burnt circuits.

Any help would be appreciated
Thanks
joey

Check filters and air flow. the pressure switch issue has nothing to do with the limit. You may ahve 3 problems.

Make sure your filter is clean first. You can't tell if the limit switch is bad by looking at it. A tech with a thermometer can tell if it is shutting off at the right temperature. But these switches are available on line for cheap, and are usually easy to replace. Simply turn off your furnace power, unplug the two power lines going to the switch, unscrew it and remove it. If replacing it doesn't help THEN call in a tech. Unless you'd rather have him install it and charge you $180 for the part that will cost you $20 online! BTW - AVOID famousparts.com for HVAC parts. I had better luck with an ebay seller called bluestang5 - he has all kinds of parts, and ships quick.