If your radiators are hot at the bottom and cold further up, this means there’s an air-lock and they won’t be heating the room effectively. Most radiators have a bleed screw at the top. The air can be released by loosening the bleed screw with a radiator key. If you have a sealed system, when you let air out, you need to put water in. This is done using the filling loop and should have been shown to you when the boiler was installed.
If you keep having to bleed your radiators this probably means there’s a leak, and you should call us.
Make sure your radiators are not obstructed by curtains or furniture and don't use radiators to dry your washing as this causes condensation that could lead to mould growth.