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this is a huge problem in these. theres not a lot you can do to prevent this, the only thing you can try is get a piece of bare copper wire and wrap it around the defrost heater under the coils in the freezer and put it it the drian hole , when the defrost heater comes on it will heat the wire and keep the hole clear, you only need to go down the hole about an inch. thats the only thing you can try, when you defrosted the ice with boiling water was it draining quickly dpown the hole or was it slow?