Our cooker hood decided yesterday that self-immolation was preferable to extracting air:

Does anyone have any tips on the best ways to clean up the wall and prepare for repainting?

Consider this too your regular reminder to always have a fire extinguisher handy – was very glad I could quickly grab a powder one and put this out, even if the stuff does go everywhere!

Sugar soap to clean and stain block before repainting

I’ve successfully used several PVA coats to seal it after scrubbing off as much as possible …. then added extra PVA to the paint as well (and do multiple coats leaving it to dry between) though you might end up painting a larger area or just do the final 2 coats without but you might find that new paint still look bad anyway depending how off colour the rest is.

I’m guessing its all plasterboard so removing the skim layer plaster would be a real pain..

I second the sugar soap and stain block. Have a look at the Zinsser range and pick the one that suits – I’ve had good results with all their products that I’ve used.

I’d try and get as much soot as possible off dry (like kitchen scourers / tile sponge) before the sugar soap or anything wet… though I haven’t used the specialist stain blockers it spreads about as soon as you get it wet and then seems to soak in to all the surrounding bits… having had to do this twice second time I spent much longer mechanically getting it off and it made the rest a lot quicker.