Cleaning the cooker to sell

imho

Get the oven cleaner from the £1 shops its in a box.Just put all the black things the pots sit on into a bag that comes with the oven cleaner and leave over night outside as sometimes the bag leaks.U can put the Oven racks in the bag as well.

Ben84

You can put the pan stands and shelves in a sealed plastic bag overnight with a few tablespoons of household ammonia. The grease will turn to black liquid and wash away easily. But it will smell strong!

As for greasy non-burnt deposits, like the ones you get on the side of the cooker and tiles behind it, I've not found anything better than borax and hot water.