To bleed radiators, follow these steps:

1. Turn off the heating system before opening any bleed valves to prevent the system from moving water while a bleed valve is open, which could suck in more air.
2. Begin on the lower floor at the radiator furthest from the boiler, then move sequentially closer in. Repeat that sequence on the upper floors.
3. Hold a bowl or rag under the bleed valves spout, slowly open the screw, and let the air escape. If a steady stream of water comes out, close the valve and move on. If you hear a hissing sound, wait until the hissing stops and water starts coming out, then quickly tighten up the bleed plug by turning your screwdriver clockwise.
4. Repeat the process with other radiators, starting with the one furthest from the boiler and working your way back.
5. Check the top and bottom of each radiator to ensure all areas of the radiator have been bled.
6. Once youve bled all the radiators, turn the heating system back on and check for cold spots or air in the system.

Its generally best to bleed all the radiators, not just the problem one, to ensure the heating system works efficiently. If you have a multi-story house, start with the radiators on the lower floor and work your way up. If you have a bungalow, flat, or apartment with just one floor, start with the radiator furthest away from the boiler and work your way to the closest.