Single Panel Radiators Btus 2 Radiators In My Living Room Only Get Hot Around The Sides And Tops. They Are Both 6ft Single Panels.?

2 radiators in my living room only get hot around the sides and tops. They are both 6ft single panels.? - single panel radiators btus

I bleed, but they are still warm. Does this mean that they are dirty. If so, what is the cleanest way to escape the wall. I am aware of the closure of the entrance / exit of the valve and let the pressure through the bleed valve. How can I prevent that the injection of water ports of entry, while I took the cooler?