After pulling the double oven out of the wall and disassembling the back to test the upper and lower thermostats (which I found to be working properly) I replaced the thermal fuse behind the display. It was inconvenient to pull the whole unit but there was no other way to be sure they were ok before the arrival of the thermal fuse. After a bit of internet research, I found that blowing the thermal fuse during self-cleaning is a common problem with KitchenAid/Whirlpool ovens (but there is strangely no mention of it in the owner’s manual).