Several local instances...one, a neighbor's electrostatic precipitator went...oh, 15 years ago. Board bad....company wanted over $300 for the board.
Puled it apart, checked it out....can't recall...op amp or regulator obviously blown...ordered two....five bucks....soldered one in, other in a ziplock taped inside the cover...still working.
About four years ago, other neighbors were in Romania visiting family. Hit the local airport on the way home, remotely cranked up the heat...all fine when they got home about 2200 hours on a January evening.
Hour later wife is pounding on my door.
Funny smell for a bit, now no heat...kids cold....looked at it, inspected the circuit diagram inside the front cover...checked voltages....looked like either a bad main relay, or failed solder joint. Pulled the board.
Apparently the solder joint had been a problem for some time with excessive heat. There was a 3/8" diameter hole burned clear through the circuit board at that relay pin.
Soldered a heavy jumper from the pin to a good part of the circuit board....reassembled....still working today, and no parts required.