How to Bleed Old Radiators

Written by christina riopelle
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How to Bleed Old Radiators
(Hemera Technologies/ Images)

There are two types of heating systems that utilise radiators. The first is a steam system. Steam originates in a boiler and circulates through the home via room radiators. Hot water radiators circulate water. Only hot water radiators require bleeding as part of regular maintenance. Air becomes trapped in the radiator and blocks the water flow, resulting in an inefficient radiator with hot and cold spots.

Skill level:

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Things you need

  • Radiator key
  • Flat head screw driver or 12-point quarter-inch socket wrench
  • Clean towel
  • Safety glasses

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  1. 1

    Feel the radiator carefully. Place your hand several inches above each chamber, also called a fin. If the radiator feels hot in some places, while other fins are cold, it is time to bleed the radiator. Safety glasses are imperative, as hot water and steam may shoot from the valve.

  2. 2

    Look for the valve. The valve is located on one of the sides of the radiator towards the top.

  3. 3

    Locate the radiator key and place it in the valve socket. If the key is not available, hardware and home improvement stores sell radiator keys. Alternately, a flat screw driver or a socket wrench can be used. Choose a quarter-inch 12-point socket wrench for best fit.

  4. 4

    Slowly turn the key in a counter-clockwise direction. When water begins to drip from the valve, stop turning the key.

  5. 5

    Wipe excess water from the side of the radiator to prevent it from wetting the floor.

  6. 6

    Descend to the basement or room where the boiler is located. By bleeding radiators, pressure in the system is changed. Open then close the boiler valve to add water to the system. Read the boiler gauge. Boilers require pressure in one-pound increments for every two feet of rise. For example, heat travels 24 to 30 feet above the basement in a two-story house, requiring a gauge reading of 5.44 to 6.8kg of pressure.

  7. 7

    Add water to the radiator if the pressure is low to restore adequate pressure to the system. This is typically the case when radiators have been bled. To avoid multiple trips to the basement, ask a helper to read the gauge or add water to the radiator. When the gauge indicates that pressure has been restored, the job is complete.

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