thermal runaways - heating failure A10T

[alfvv12]

hi.
i cannot print. a10t is inly some weeks old.

fir some days printer has abnormal stops after 2 to 3 hours. message "thermal runaways".

now only some layers are printed, then this error:

the bed heats up to correct temperatur e of 65 deg. C.
after begin of printing the temperature is continuously descending under 40 deg.C.
then printer stops and error "heater failure" is shown.

is bed heater modul defect?
or heating plate?
or what could it be??