And the furnace tech has just informed me that the replacement board is $550. That's right, Five Hundred Fifty Dollars, American. ...That's my money for a new mattress...that I didn't actually have and was putting off the purchase of therefore.
I'm unhappy. I might be able to fix the bad board myself, if it's stupid enough and if the active components aren't bespoke and don't have their identifying marks obscured.* What I can't do is warrant that it'll have the same reliability and safety as the OEM part. These days, that counts on matters like insurance. It's why there's probably no "core credit" for the old board, too.
* Diodes, transistors and integrated circuits use a somewhat-scattershot assortment of European, JEDEC, trade-association and manufacturer's numbers that usually resolve down to one of a few thousand replacement parts per component type. A competent electronics tech can usually find them. But some makers remove the numbers and others -- big, vertically-integrated operations, mostly -- build their own parts and often won't sell them. Passive components like resistors, capacitors and (less so) inductors are marked with common color codes or simple numeric shorthand. Transformers? Yeah, good luck with that. Most OEM ones have nothing other than not-very-informative color-coded leads.