If you have air in your central heating radiators, there are a few things you can do to get rid of it. First, check to see if the bleed valve on the radiator is open. If it is, turn it clockwise until it is closed. Next, find the fill valve on the boiler and open it until water comes out. Once the water starts flowing, close the fill valve and turn on the boiler. The water will push the air out of the radiator and into the boiler.
You can also use a radiator key to manually open the bleed valve. Place a bucket beneath the valve and turn it anti-clockwise with the key until water starts flowing out. Let it flow until you hear no more gurgling sounds, then close the bleed valve and turn on the boiler.

Finally, you can use an automatic air elimination system to get rid of any remaining air in your radiators. These systems use pumps and sensors to remove air from your radiators before it becomes an issue.
If you follow these steps, you should be able to get rid of any air in your central heating radiators.

There are two reasons you might need to bleed radiators: if it’s cold at the bottom but not the top, or if the entire radiator is cold. If it’s just cold at the bottom, that means there’s air in the radiator. Radiators work by circulating hot water from the boiler through metal fins. The heat from the water transfers to the fins and then to the room. If there’s air in the radiator, that transfer of heat can’t happen properly and your whole house will be colder as a result.