Put burners in ziplock bag, add 1/2 cup of ammonia and let sit overnight, and in the morning wipe clean with a sponge/rag! I do this with my oven racks too. Don't try with aluminum, but if you get that black stuff on the bottoms (or inside if you *really* burn it) of stainless steel pans, it works great on them too. I just use garbage bags for the really big things.
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Clean Stove Burners with Ammonia: take 1/4 cup of ammonia and seal it up with one of the burners in a large ziploc bag. You only need a little ammonia in the bag. It is the fumes from the ammonia that dissolves all of the grease and hardened oil. You don't need to soak it, it just needs to be sealed up with the ammonia fumes. Leave it outside on a cookie sheet overnight.
How to clean burner pans with WD-40 and if it works or not! Truth on the best way to clean stove drip pans.