How to Bleed a Cast Iron Radiator

If your cast iron radiators make clanging noises, there may be air in the system. Another sign of air in the system is if the radiator is hot on the bottom but cool on the top. You can remove the air in your heating system by bleeding your radiator. All you need is a radiator bleeder key and a bucket to catch the overflow.

Things You'll Need

• Radiator bleeder key
• Bucket
• Old rag

Instructions

1. Turn off the boiler. Find the switch located on or near the boiler itself and move it to the off position. Do not attempt to bleed your radiators until your boiler is turned off.

2. Start with the radiator closest to the boiler. Locate the bleeder valve. It is located on the side of the radiator, near the top, usually near the back. The end of it looks similar to the end of a valve on a bike or automobile tire, only much larger.

3. Place a bucket and rag under the bleeder valve to catch overflow water. There won't be much, but there will be some dripping.

4. Insert the bleeder key into the end of the valve.

5. Turn bleeder key half a turn counterclockwise.

6. Turn bleeder key clockwise to close, when a steady stream of water flows from the bleeder valve.

7. Move on to the radiator that's the next closest to the boiler, and repeat Steps 3 through 6. Continue until all radiators are bled.

8. Turn boiler back on.

Tips & Warnings

• Radiator bleeder keys are available at home improvement stores.

• Do not attempt to bleed your radiators until your boiler is turned off.