Nah not new board, if you are in Europe, send those parts to test it, I need only panel, buttons board and that mcu controller, if I manage to dump it that there is no fix charge, just shipping and return costs. I'm curious if they use open source for that ic. Example I was able to dump RE8500 and controller and flashed new one and work. I did that because of those issues. But in 10 years didn't happen.
Case is too strong to fail and well cooled if interior temperature reaches 400 Celsius.
If you don't find fix solution just send it in.
Add close look of that atmel mcu.