My furnace stopped working again yesterday. Luckily I was able to get it running again myself this time. Like last time, I noticed it being a bit cool and saw that it was a couple degrees cooler than the thermostat setting. The furnace was throwing the same code 31, indicating the pressure switch. I blew out all the tubes I could connected to the switch or the condensate trap. I cleaned out the trap, which had plenty of gunk once again, this time spending more time on it. I did so by running water through it, shaking the water out with any gunk, and repeating until there didn’t seem to be any more. Putting everything back together and running it, it was still behaving the same way, rumbling for a while and throwing the code after 15 seconds. After several tries, I gave up, worrying I’d have to call the furnace company again. But then I remembered reading last time that the trap needed to have water in it, and could either be prefilled or get filled by running it. I turned it back on, figuring its 15 minute cycle of trying again might eventually fill it. As it happened, it began putting out heat the first time, and kept working since. So maybe I’ll just have to clean out gunk every few weeks until hopefully it clears out of wherever it’s coming from.