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I wouldn't say normal, but also not uncommon especially if you're someone that's good with tinkering.

Basically if the furnace is fairly old, parts start wearing down and requires replacement or fixing. So you get to a point where you have to fix things more often because all the parts have reached end of life. Often it'll be a small thing like maybe you need to clean the flame sensor, and then after that your negative pressure sensor goes out so you have to fix that. Those are all safety measures, so the furnace might be working perfectly fine but the control board thinks it's unsafe, and shuts down, which is the correct thing to do. There's a possibility the wire juggling is bypassing some of those.

But a lot of those items you can do for basically free or really cheap, so it's not appealing to throw $2500 on a whole new one or to get a professional in to charge you $300 for the same fix. Furnaces also need to be services regularly, ideally yearly to check everything is good and prevent failures at inconvenient times, which many just can't afford or don't want to spend the money on. If $2500 is a lot of money for your parents, it's just a small tradeoff that yeah it might go out every now and then and you fix it for so much cheaper.