How to Bleed a Radiator

Take care of your home heating system by learning how to safely and effectively bleed a radiator.

checking radiator
Photo:

zoranm / Getty Images

Project Overview
  • Total Time: 30 minutes
  • Skill Level: Beginner

When hot water flows through a radiator, it heats up the appliance, which in turn transfers the heat to the air in the room. However, if air gets inside the radiator, it can prevent the water from circulating properly, resulting in reduced efficiency, higher heating bills, and significant temperature differences throughout the home.

In most cases, this issue is easy to resolve by bleeding the radiator. Bleeding the radiator refers to the process of opening the bleed valve and allowing the air inside the radiator to exit. Once the air has been released from the system, the water will begin to circulate through the radiator properly, restoring the heat to the room. This is a fairly common task that should be completed at least once a year to ensure that there isn’t air in any of the radiators in the home. Use this guide to learn how to bleed a radiator and make this job a regular part of your annual home maintenance.

When to Bleed a Radiator

It’s recommended to bleed the radiators in your home at least once per year, but there are also several common signs that can indicate the radiators need to be bled. One common symptom is that a radiator feels colder at the top than it does 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 entire radiator is cold, the system might have trapped air in the pipes that's 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 be a result of a different problem, like a leaking water line. 

How to Bleed a Radiator

Bleeding home radiators is a basic task that most DIYers can handle. It doesn’t involve a lot of tools or equipment, and it takes very little time. In addition, it’s a maintenance task that really only needs to be completed about once a year. Follow these steps to learn how to bleed a radiator to keep your heating system functioning properly throughout the year.

What You'll Need

Materials

  • Gloves
  • Radiator key
  • Bucket
  • Rag or cloth

Instructions

Step 1: Turn Off the Heat

The first and most important step of this process 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. 

Step 2: 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.

Step 3: 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.

Step 4: 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. 

Step 5: 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 the further away from the boiler to the closest. Start on the lowest floor of the home and move up one floor at a time. 

Step 6: 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.

Step 7: 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.

Radiator Bleeding 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 the 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 will 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 cannot 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 the best you can to adhere to this order to optimize the results.