burner has run 980 hours now. with 60% power (= 30 kW)
i clean it only with a spoon and a vacuum-cleaner. not with a hammer.
i guess it broke, because it got too hot at this place, although i always removed sintered material (very less)
and i am quite sure, that was the reason for the "opto sensor warnings" i had a few times. because the burner could not keep the pellets glowing with this hole in his cheek