1. Above my radiator the wall has discoloured

Density or discolouration of walls and/or ceiling above a radiator is called "fogging" and occurs for the following reasons:
When heating a room, cool air warms from the bottom, passes the radiator and then rises upwards. The air receives the heat from the radiator panels or from inside the convector. This is caused by dirt particles in the air which are flowing from the bottom to the top of the radiator. The radiator itself has no loose dirt particles or dust, which could effect a discolouration. After priming and final coating the colour is baked, after which the radiator is packed. During heating the radiator is filled with water, which cannot lead to the complaint mentioned above.