My Furnace (a Rheem Criterion II Gas Furnace - model RGLH-07EAMGR) has had a problem for a while that we've just been living with but I can finally afford to do something about it.
What happens is that it will run fine for a while (hours, days, even weeks -- pretty random), and then it will stop running. I go out and check and the 'OK' LED is flashing 3 times and then off, 3 times and then off. The troubleshooting guide says this means "The limit switch is open".
What I have figured out is that if I wiggle the wires that attach to the pressure switch just a little bit (picture below), then put the covers back on, the furnace will turn on again and run normally for a while. Then, at some random time in the future, it will shut off and be back on the 'OK' LED flashing.
Based on my research, it sounds like Pressure Switches are usually an indicator of a problem rather than being the problem itself. But since wiggling that wire seems to reset things, I wonder if in this case it is the Pressure Switch? Or is it possibly actually the Limit Switch that needs replacing (I've never actually tried wiggling those wires)? What's the best way to troubleshoot this?
I will probably end up calling in a pro to take care of this, but I mostly want to understand so I can make sure I'm not getting ripped off..