The Tool Barn

Bleeding a Hot Water Heating System

If you have hot-water heat (radiators), you will need to bleed the system from time to time.  This is necessary to ensure the proper flow of water through the system.  This applies to systems that use standing radiators or base-board radiators.  One note of Caution: If you wait until the system is in use, the water that comes out will be HOT!  Also, if there is air in the system it may blow the water around a bit.

Items needed:

Radiator key or screwdriver (depends)
Cup or shallow dish
Air hose from fish tank (optional)

Safety Suggestions and Tips
Be careful, escaping water may be hot!!
Level of difficulty

Time Required:
 1 hour


Open base board
Open base board

Step 1:

Locate all of the bleed valves in your system.  If your system is a base-board system you will have to open the door on the front of the end piece to find the valve.  If the valence on the front of the radiator is too long you may have to pull off that piece as well. The valves on the base board systems are generally located where the pipe comes through the floor.  The valve on a standing radiator is usually on the top at the end.  Take note of the type of tool that will be necessary to open the bleed valve.  Some valves use valves that are opened with a straight-edge screwdriver.  Some use a square fitting that requires a radiator key.

Standing radiator
Standing radiator

Step 2:

Start on the radiator that is farthest away from the boiler.  If your house has a second floor, start there.

Baseboard bleeder valve
Baseboard bleeder valve

Step 3:

Place something under the spout: the amount of space available around the spout will dictate how big a container you use.  If there seems to be no room, a piece of air hose from a fish tank sometimes works.  Remember, the objective is to get the air out, not run out huge amounts of water.  Using either a radiator key or a small screwdriver, turn the screw until air and/or water starts to run out.  Leave the valve open until you get only water.

Boiler bleed valve
Boiler bleed valve

Step 4:

Close the valve and then go to the next radiator in the sequence, working you way back towards the boiler.  When you have done them all, go back to the one you bled first and bleed it again.  If you get only water, you're done.  If not, repeat the process.

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