How to Bleed a Radiator

When to Bleed a Radiator

It’s recommended to bleed the radiators in your home at least once yearly, but several common signs can indicate the radiators need to be bled. One common symptom is that a radiator feels colder at the top than near the bottom. This is a sign that air is preventing the water from circulating properly. Another symptom is that the air trapped in the heating system causes the radiator to rattle or make odd gurgling noises.

Less common signs that you need to bleed a radiator include the entire radiator being cold or mold or damp spots around the home. If the whole radiator is cold, the system might have trapped air in the pipes, restricting the flow of hot water to the radiator. Mold and damp spots can indicate the temperatures throughout the home are imbalanced, leading to condensation. However, mold is a more generalized symptom and may result from a different problem, like a leaking water line.

What You'll Need

Equipment / Tools

Gloves
Radiator key, screwdriver, or wrench
Bucket

Materials

Rag or cloth

Instructions

How to Bleed a Radiator

Understanding how to bleed a radiator is a simple and essential task that most DIYers can handle. It doesn’t involve a lot of tools or equipment, and it takes very little time. Follow these steps to learn how to bleed a radiator to keep your heating system functioning correctly throughout the year.

Turn Off the Heat

The first and most crucial step of how to bleed a radiator is to turn off the heat. Not only can an active heating system introduce more air into the line, but you also need time for the heat to dissipate so that you don’t burn your face or hands when you remove the bleed valve. If the radiator is still hot, removing the bleed valve will result in steam and near-boiling water spraying out of the valve in your direction. Turn off the heating system and wait for the heat to dissipate. Check to ensure the radiator is cool before proceeding.
Prepare the Area

While you're waiting for the radiators to cool down, you can prepare the area by placing a bucket at the base of the radiator to catch any water that exits through the bleed valve. Now is also a good time to grab an old rag or cloth to help contain the spray of water droplets and to clean up any water that spills on the floor.
Open the Radiator Valves

Check to make sure that both the intake and exit valves of the radiator are open before inserting the radiator key into the bleed screw. If you don’t have a radiator key, you can usually find one at the local home improvement store. Alternatively, you might be able to use a screwdriver or wrench to operate the bleed valve. With your tool of choice inserted into the bleed screw, turn the screw counterclockwise to open the valve.

As you open the valve, you should begin to hear a hissing sound as the air escapes the radiator. Make sure your cloth and bucket are ready, and don’t be surprised when a little bit of water starts to drip out of the valve. Use the cloth to catch the drops, and keep your eye on the valve.

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Close the Bleed Valve

When all the air has been released from the radiator, you will see a steady stream of water begin to pour out of the bleed valve. If the bucket is in the right position, you should be able to catch any water before it can soak the floor. Tighten the bleed valve to stop the flow of water by turning the bleed screw clockwise. Check to make sure that there aren’t any leaks, then use your rag to wipe up any water that missed the bucket.
Repeat for Each Radiator

Empty the bucket and wring out the cloth or rag, then proceed to the next radiator in the home. Repeat this process with every radiator. Work from the radiator that is further away from the boiler to the closest. Start on the lowest floor of the home and move up one floor at a time.
Check Pressure Level of Boiler

After bleeding every radiator in the home, check the pressure level of the boiler system. It should have a pressure level of around 12 to 15 psi to function properly. If the pressure level is too low, top off the boiler by opening the water feed valve until the pressure gauge reaches 12 to 15 psi. If your boiler has an automatic fill system, this shouldn’t be a problem.

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Turn on Heat and Test the System

Turn on the heating system and wait for the water to begin circulating through the radiators. After about 20 minutes, check each radiator to ensure that they are producing heat and that the heat is being evenly dispersed from the bottom to the top of the radiator.

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How to Bleed Radiators in the Right Order

Most homes that rely on radiators for heat will have more than one radiator throughout the home. In many cases, radiators are installed in the main rooms of the home, including the kitchen, living room, dining room, basement, and bedrooms. When you bleed one radiator, it's recommended to take the opportunity to quickly bleed all the other radiators in the home.

Start this process with the radiator on the lowest floor of the home, located the farthest from the boiler. The next radiator should be next closest to the boiler on the same floor. In this fashion, work toward the boiler until you have bled all radiators on the lowest floor. You then need to move up one floor and start the process with the radiator furthest from the boiler. Work toward the boiler until all radiators have been bled, then move up a floor and repeat this process as needed.

If you can't bleed the radiators in a specific order for any reason, you don't need to worry. Bleeding them out of order shouldn't cause any significant problems. Just do your best to adhere to this order to optimize the results.