The heatsink fins accumulate dust from the cooling air. Since a dusty heatsink is less efficient at cooling the drive, overtemperature faults become more likely. In a “normal” environment (not dusty, not clean) check the heatsink annually, in a dusty environment check more often.
Clean the heatsink as follows (when necessary):
NOTE: If there is a risk of the dust entering adjoining equipment, perform the cleaning in another room.
Source: Daikin (oslo.daikinapplied.com)