How to bleed hot water systems

Written by dale yalanovsky
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How to bleed hot water systems
Used to heat residential and commercial buildings (Comstock/Comstock/Getty Images)

Hot water systems are primarily used for heating in both residential and commercial buildings. There are two main types; a gravity fed system and a hydronic heating system. Hydronic systems use a pump to pressurise water and send it through pipes and into radiators. This system has all but phased out the much older style gravity heating system. Bleeding each of these systems means locating the bleeder valves on the heating pipes, and purging them of trapped air.

Skill level:

Things you need

  • Pliers
  • Cup or small container

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    Bleeding hot water systems

  1. 1

    Locate a bleeder valve on the hot water system piping. Ideally, locate the valve that is along the pipe run which is on the opposite end of where the heating pipe enters the building. The valve will be found adjacent to baseboard radiators, and will look like a jutting pipe nipple with a nut attached to it.

    How to bleed hot water systems
    Locate the bleeder valve (Thinkstock Images/Stockbyte/Getty Images)
  2. 2

    Turn your thermostat up 15 degrees so that the system calls for heat. This action gets the water flowing through the pipes, and is essential for proper bleeding.

    How to bleed hot water systems
    Turn the thermostat up (Jupiterimages/Pixland/Getty Images)
  3. 3

    Place a small container or cup beneath the valve that is to be bled.

    How to bleed hot water systems
    Place a container for water collection (Jupiterimages/ Images)
  4. 4

    Turn the bleeder nut slowly to open the valve.

    How to bleed hot water systems
    Turn the bleeder nut (Jupiterimages/Goodshoot/Getty Images)
  5. 5

    Listen for hissing air to escape and be bled out of the pipes. This is a good sign..

    How to bleed hot water systems
    Hissing air is a good sign (Siri Stafford/Photodisc/Getty Images)
  6. 6

    Catch any water with your cup or container that begins to flow out of the bleeder valve. The hissing will stop at this point, and the valve can be closed.

    How to bleed hot water systems
    Catch water in the container (Cameron Spencer/Photodisc/Getty Images)
  7. 7

    Repeat this procedure on all the bleeder valves, working your way along the pipe run towards the point where the heating pipe enters the building.

    How to bleed hot water systems
    Repeat on all bleeders (Thinkstock Images/Stockbyte/Getty Images)

Tips and warnings

  • Once the bleeder valve is closed, wait a few minutes and then feel the surrounding pipes for heat. If there is no heat, proceed backward along the loop, bleeding out each section of pipe until all the air is purged from the system. Once the air is purged, water will flow and the pipes will get hot.
  • Be careful. You will be dealing with very hot water. Take precautions to limit any spraying water by always making sure to open the bleed valves slowly and carefully.

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