Symptom: The ice maker in the refrigerator was not working. The previous owners of the house mentioned that the ice maker hadn’t worked for a long time.
Solution: The ice maker actually has diagnostic terminals that you can probe with a multimeter. By doing this, you can detect various different issues, including whether the inlet valve has failed. This was exactly the issue with this refrigerator. Getting a replacement valve cost $20 from Amazon, and took half an hour to replace. (Note: this was strikingly similar to the previous issue of the dishwasher inlet valve failing. It’s possible that the two failures are connected, perhaps due to a power surge?)