What parts are good to keep on hand for a gas furnace? I have 2 Trane/ American Standard gas furnaces in the basement, about 7 years old. I just replaced the pressure switches, and the ignitor on one of them (went bad at 6 PM on New Year's Eve...). So today I am ordering a spare ignitor, as it will fit either furnace and I DON'T want to pay another $500 emergency call-out for such a simple part. So what else should I keep on hand? I.e., what items have a fair- chance of total failure, can be installed by a DIY-er, and aren't extremely expensive? In my experience, pressure switches are pretty inexpensive, but they can be cleaned / blown out, so you have time to order a new one after they start going bad.
If you reply, I would greatly appreciate it if you could also respond directly to my email address. Thanks in advance, - Erik snipped-for-privacy@yahoo.com