Can anyone tell me how you can remove very heavy built up lumpy carbon from baking trays and underneath of grill pans please.

Soaking in cold water with a splash of washng up liquid, for at least 24 hours, then a good clean, usually helps remove most things.

Daisy

Soda crystals in Very hot water usually helps, I have also used one of those blade thingies that you use to get paint off windows but only on enamel baking trays, hard graft but does work to get the heavy lumps off then a brillo pad!
Chris

Give a soak in v hot water and dish water tablet then use ovenpride oven cleaner from sainsburys leave over night great stuff I paint it on swith old brush. Comes up like new everytime

I clean the oven shelves by putting them in a bath of really hot water with Biological washing powder. Leave them to soak for a couple of hours and then give them a rub with a scouring pad. Does the trick!

Ditto but with one of those wire scouring things spontex is it and i use Biotex to soak them in.
(or chuck the tray and buy a new one) or was that just the spuds in a saucepan trick I once boiled dry??

I put them on the hob with bio washing powder and hot water then boil until the water reduces. This usually does the trick and works well for burnt on food in saucepans etc.