In the part few months a permanent stain remains in my toilet bowl just where the water enters from the cistern. I have tried bleach and jiff to no avail. Can anyone advise me?
its usually limescale that coats the porcelain and can then hold salts (usually metallic) from the water and cause the stain. Get limescale remover, the thick kind and treat the area over night for four or five nights, this should sort it.
Get a mop and mop out the pan til it's dryish then get some Harpic limescale remover and leave it in for a bit before mopping round with it, it gets ghastly loos like new, otherwise if that doesn't work as Conne says a new loo:)
it happens to me too, there seems to be a spate of water that comes through the pipes with the salts in then it stops again, i guess it gets washed from somewhere in the main system.
be careful playing around with spirits of salts. if you decide to use it, use old clothes thick rubber gloves and eye protection. keep the bottle tightly closed and put away safely.
As the problem is with the area where the water runs down, rather than in the toilet bowl the answer will be something that you need to add to the cistern. I don`t know what though - bleach?
You could add those blocks that are designed to be immersed into the cistern. I have seen those stains in hotel bathrooms. It`s usually something in the water (a mineral or whatever). There isn`t a lot that can be done if the stain is in an area where there is running water rather than still water.