How to bleed a boiler heating system

Written by seth amery
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How to bleed a boiler heating system
When boilers develop air pockets, radiators must be bled to alleviate pressure. (boilers image by JCVStock from

A standard water boiler system includes radiators, carrier pipes and a boiler furnace. Air pockets may develop from time to time due to the rising heat. When this occurs, the radiators require bleeding to alleviate the pressure. Bleeding is as simple as twisting the correct valve on the radiator, but the process can be time-consuming without the help of another person. If you have a partner, one of you may call out the changes in the gauge as the other tends to the radiator.

Skill level:

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Things you need

  • Towel
  • Safety glasses
  • Radiator key
  • Plastic cup
  • Pliers
  • Screwdriver

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  1. 1

    Check for heat conduction. There is an air pocket if multiple chambers, or fins, are cold while the radiator is running. However, it is not uncommon for one to be cold while others are not.

  2. 2

    Read the gauge on the boiler. Keep in mind that a pound of water pressure is necessary for every two feet that the heat is to rise. Typically, a two-story home should have 5.44 to 6.8 Kilogram of pressure.

  3. 3

    Put a towel on the floor next to the radiator. Hold a plastic container under the valve. These will protect the floor. Wear safety glasses to avoid burning your eyes.

  4. 4

    Find the valve key. Obtain a substitute at a hardware store if there are none. Use pliers and a flathead screwdriver if this is not possible. Insert the screwdriver into the socket. Grasp the handle with the pliers. Slowly turn the key—only a short distance is required. When pressure is relieved, you will hear a hissing sound. The valve is open when some water seeps out.

  5. 5

    Read the gauge again. Open the boiler valve, located a hair above the furnace, and close it again. This allows some water to release into the system. Repeat until the gauge is normal.

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