Brown coating on bottom of cooking pot

Try boiling up some vinegar , ideally white although it doesn't matter, just dont let it boil dry.
Alternatively - but this does pong- an enzyme stain remover such as ACE - will generally lift crusty burnt on bits.

I use ordinary soap powder boil it up and most stains an d burns will just disappear

My go-to would be washing powder. You just need about a desert-spoon of it and boil it up.
I think maybe this is what you are saying BlueBelle?

Yes exactly Notspaghetti what ever washing powder is at hand it strips it off very quickly as you boil it up and leaves it sparkling

Obviously you have to then wash it really well - don't just rinse it!

Fairy Skip the Soak spray. It’s very effective and you can clean worktops, hobs etc too.

Haven’t tried it on saucepans but roasting dishes have responded well to that Pink Stuff you can get for stains on clothing. Sprinkle a good amount of powder onto the surface, add boiling water - it’ll fizz and bubble - and leave to soak for an hour or two or overnight. Then give it a good clean.

Just boil up some washing powder or dish washer powder and leave for a while and it will rub off perfectly.

Soda crystals and soak in hot water overnight

I have 2 old cast iron pots that have a brown colour to the inside. Yesterday, I poured half a pack of Soda bicarb into each, along with a little water to wet it, and left it overnight. Washed, and rubbed with a sponge this morning. The enamel looks so much better; I have not seen them look so good in years!

Great tips and our family seem to only have two cooking heats, especially DH, off or boil!

Washing soda and hot water and bring to the boil.

A soak in bleach and cold water will return cast iron interiors to their proper colour. If stuff sticks to my pots I soak them overnight in water and detergent and then scour them with wirewool.