how to sort cellar

It sounds as if the brickwork blocking off the old coal shoot is leaking, the yellow/Brown stuff will more than likely be Iron oxide and limescale left behind by the dripping water.

Are the cellar walls dry is so then you just need to sort out the sealing of the coal shoot and all should be well.

 

Often a cellar is below ground level and not really designed to keep things perfectly dry. So, no great surprise there.

Assuming it's as simple as that in your case, what you need to do is find a way to keep the water oot. And the usual solution is 'tanking'.

Tanking takes many forms from a brush-on bitumen emulsion (it'll help, but likely not cure) to 'slurry' types. These are cement-based, so set chemically rock-hard and adhere properly too. So better.

There are other solutions too, but they usually involve building a second internal wall to completely isolate the room from the ootside.

So, assuming it isn't down to a fault like a burst drain or crack in a wall, tanking is what you'll likely have to do.

Bear in mind, tho', that cellars - by their very nature - have little or no natural ventilation, so will always tend to be a bit stale and dank unless you sort that oot too....

 

Puddle of water on the floor, brown stains on the wall. Sounds like the bloke chained up down there is on a dirty protest.