this is probably no good for you but it works, and damn well, particularly for ovens in houses rather than commerical, and only on the shelves, but hey it saves time and effort...
fill bath with boiling hot water and about half a box of biological washing powder.............put shelves and trays (anything removable and not self cleaning) in the bath of solution ensuring the water covers all......leave overnight....next day, nearly all baked on hard to remove stuff just falls off........and the rest is easy to rub off with scourer!!
Did my own oven a few months ago and shelves were like new..........it was a miracle.
Had to do mine a couple of times as (ashamedly) I had only done them a few times in the 4 years I have had the oven. :
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