How to Bleed a Boiler & Radiator

Updated February 21, 2017

A hot water system that uses a boiler and radiators to provide heat requires yearly maintenance, which will require you to bleed the system. When a hot water system has been running for long periods of time air can get into the system, which will need to be purged. Before bleeding a radiator and boiler, turn off the boiler.

Turn off the boiler to your heating system.

Place a small bucket on the side of the radiator under the bleeder valve.

Insert a radiator bleeder key into the bleeder valve of the radiator.

Turn the bleeder key counterclockwise half of a turn to open it. When the valve opens there will be a hissing sound as air escapes.

Turn the bleeder valve clockwise half a turn to close it when water starts to leak out of the valve.

Repeat steps 1 through 4 on the rest of the radiators for the heating system.

Attach a garden hose to the drain valve on the boiler.

Place the hose in a bucket or a drain on the floor, or run it outside.

Open the fill valve to let water into the boiler and then open the drain valve. Open the valve by turning it clockwise.

Let the water drain out of the boiler until no air bubbles come out of the garden hose.

Close the drain valve and the fill valve. You can then remove the garden hose and turn the boiler back on to complete the project.


Clean up any water that has got onto the floor with a rag or towel.


If you do not turn off the boiler the hot water coming out of the radiator or boiler can cause burns.

Things You'll Need

  • Small bucket
  • Radiator bleeder key
  • Garden hose
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About the Author

Cameron Easey has over 15 years customer service experience, with eight of those years in the insurance industry. He has earned various designations from organizations like the Insurance Institute of America and LOMA. Easey earned his Bachelor of Arts degree in political science and history from Western Michigan University.