Those buttons are in the same region as the display. Are they completely waterproof?

I recon you'll be right in the end. I managed to open the top part (well, the most of it anyway) and found impressive amount of rubber seals, contactless pole buttons and other precautions to make the control panel water-and-vapor-proof. All those, as apparent from the picture above, also impressively failed because I found plenty of water in there too. Whole contraption reminds me modern mobile phones, which I repair more commonly. Plenty of glued parts and zero thinking about repairability. Hey, it would be even much easier to move the control panel UNDER the pot and heat pad, instead above, to keep it out of vapor way and ease everyone's life. But what do I know, I'm not a German engineer.
Anyway, considering all those seals and amount of water it's apparent it would need weeks to dry out completely in closed state. What I'm gonna to do now is to dry the thing out perfectly, keep whole panel out of the body of appliance and use the device a few times this way, just to be sure how the moisture in the panel affects the thing. I bet it will behave nicely again...

 

So maybe the descaler damaged the seal, do you think?

 

Nah, no way. I believe the time and usage did. That control PCB on the first pic (water inside the LCD is apparent) is supposed to be closed and sealed in that dismantled box on the second. Descaler would hardly affect that. If there will be continuing misbehaving after this, then there is another failure in the appliance, which could be connected to the descaling. I still didn't manage to find any thermal fuses or sensors in the boiler part of the device.

 

Bloody hell! It didn't help! The PCB is dried out, I pulled it out of the body on the cable to keep it from vapors and boiled another brew. Again, ~two cups of water remained in the tank. I spent way to much time with $200 appliance already but I just hate to give up things.

 

. Again, ~two cups of water remained in the tank.

Are you sure that’s not normal? The Bunn machine I’m repairing holds two pots worth of water hot at all times. Pouring a third pot in the reservoir triggers an overflow through the coffee grounds to make a pot. I know your machine is very different.

 

Hello,

One i had repaired had the same problem. It was the thermal cutout switch.
This is not the same thing as the thermal fuse which looks like a thin bullet. The thermal cutout switch looks like that other picture far back in this thread with the two terminals sticking up. It is part meal part black body with two terminals. For the one i had, the thermal switch clamped onto one of the tubes. When the tube got empty the temperature went up and the cutout switched off. The only thing left on then was the heating plate on the bottom to keep the coffee warm.

If something goes wrong with the thermal switch the thermal fuse might blow out and then it has to be replaced. That should only happen if the thermal switch stays 'on' all the time though so it sounds like that's not the problem, only the thermal switch might be bad or became loose.

But wait a minute. If it became loose, then it would most likely stay on too long not too short.
The thing to do then is to measure the voltage across the thermal switch with an AC meter. See if or when it turns on or off. It could be that the switch just becomes too sensitive and is turning off too soon.
Note that any sludge would probably act as an insulator. That would also mean it would stay on too long.
Perhaps the switch was not working right for a long time and the sludge kept the appearance of it working right.