I was reading through the
excellent troubleshooting thread and reminded of an issue I was having with my Goodman high efficiency furnace. It was a couple years old and it kept cutting out. I would run for a while, then stop for a while, then run for a while... It was throwing a gas valve code and then it started not running more than it was running so I called for service (under warranty, thankfully). The tech checked the system out and one of the drain tubes for the heat exchanger was full of water. He cleaned out the tubes, put it together and it ran fine. Was near the end of the winter, didn't think much about it.
Next winter, I had the same issue - it worked for quite a while, then started locking out. When checked, water in the tubes. It only happened a couple of times and clearing the tubes solved the problem so I didn't think much more of it.
When it started for the third winter in a row, I started to suspect something might be up

(OK, so sometimes I'm a slow learner). Luckily the installers left behind all the documentation including the installation instructions. So I started to read them. Lo and behold, there are two drain ports - one for horizontal installations, one for vertical. It most come configured for horizontal from the factory. So I swapped ports and haven't had a single issue since (for two winters now). D'oh!
And yes, I read through and double checked everything else in the install guide just in case! Don't always take the error code at face value and don't always assume the last guy did what he was supposed to do. Probably obvious to the pro's in here, but it's something for us enthusiasts to constantly remind ourselves