This is the second time this issue happened. Right after the first year our freezer side frosted up and wouldnt keep things cold. Had a $200 repair and was told it was the defrost heater. I have the same issue (2 yrs later) with frost in the back and when I took the measure to defrost the back, it worked for several days before frosting and warming up again. Am I safe to say it is the defrost heater? I have ordered the part and can safely repair it myself but am not as qualified on the diagnostic. (I worked for and repaired in factory whirlpool and all their brands of washing machines.). Any inside advise is helpful:D