If one radiator is cold at the bottom but hot at the top, the blockage is inside the radiator itself.
To prevent future blockages, make sure to: how to unblock central heating pipes
This is the most common cause. Over time, water reacts with the internal steel of your radiators. This creates iron oxide dust. The dust mixes with water to form a thick, black sludge. 2. Limescale Buildup If one radiator is cold at the bottom
If the blockage consists of sludge or limescale, a chemical flush can dissolve it without dismantling the pipework. Tools Needed how to unblock central heating pipes