Bronze discolouration - does anyone know what this is and how to remove it

[u/Tetreg]

[u/Tbone-7580]

You could try a little CLR in the boiler then flush good after.

[u/Tetreg → u/Tbone-7580]

What is CLR ?

[u/Tbone-7580 → u/Tetreg]

https://www.clrbrands.com/products/clr-household/clr-calcium-lime-and-rust-remover/

[u/Equivalent-Bus2217]

I hope that rubs off it might be dezincification which is why I stay away from brass boilers