How to Bleed a Radiator

Keep your home's heating system in top condition in 5 simple steps.

By
Timothy Dale
Timothy Dale

Timothy Dale is a home repair expert and writer with over a decade of hands-on construction and home improvement experience. He is skilled in residential, commercial, industrial and institutional plumbing, electrical, carpentry, installation, renovations, and project management.

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Updated on 02/25/24
How to bleed a radiator

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In This Article
Project Overview
  • Working Time: 15 - 30 mins
  • Total Time: 1 hr, 30 mins - 1 hr, 45 mins
  • Skill Level: Beginner
  • Estimated Cost: $0

There are many home maintenance tasks that are important to stay on top of to ensure that your home continues functioning properly. One such task is bleeding the radiators about once a year to release air that may be trapped in the system.

When the temperature outside begins to fall, it's imperative that your heating system is capable of producing enough heat to keep you and your home warm throughout the winter months. However, if one or more of the radiators remain cool or they are significantly warmer at the base than they are at the top, then the problem is likely air trapped in the radiator fins. This prevents hot water from circulating properly and reduces the overall heat output of the unit.

The fix for this issue is relatively simple, but it's necessary to take your time with each step to avoid introducing more air to the system. It's also important to note that if you rush this job, there is a risk of injury from scalding water. Use this guide to learn how to bleed a radiator and restore heat to your home.

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Before You Begin

Caution and preparation are key to succeeding with this maintenance task. Make sure the heat is turned off, either by using the emergency shut-off switch or by simply turning the thermostats down. If you leave the heat on while bleeding the radiators, there is a chance that you may introduce more air into the system.

Wait about an hour after turning off the heat before you begin. This will give the heating system enough time to cool down. Gather one or more towels and a bucket to help catch any water that escapes from the bleed valve. It's also recommended to have a set of work gloves that can protect your hands from hot water.

What You'll Need

Equipment / Tools

  • Bucket
  • Work gloves
  • Radiator key

Materials

  • Towels

Instructions

How to Bleed a Radiator

  1. Remove the Cover and Locate the Bleed Valve

    It's recommended to take this opportunity to bleed all the radiators in the home. Start on the lowest floor at the radiator that is furthest from the boiler. Not all radiators have a cover, but if yours does, then remove the cover to access the bleed valve. This small valve should be located at the top of one side of the radiator.

    To operate the bleed valve, you will need a radiator key, which can be purchased online or at a local home improvement store. If you don't have a radiator key and don't want to purchase one, you can try to complete this job with a set of needle-nose pliers or a flathead screwdriver.

    If your radiator doesn't have a bleed valve, then it may be a steam radiator. Steam radiators have an air vent that automatically releases trapped air, so you don't need to bleed them. Though the vent can sometimes get plugged when people paint over it.

  2. Open the Bleed Valve

    Put your radiator key on the bleed valve and turn it counterclockwise about half a turn or until you start to hear the familiar hissing sound of air escaping. At this point, a little bit of water may drip from the bleed valve, so it's good to have a cloth, towel, or rag on hand to catch the drops.

    For those that have a steam radiator with a plugged air vent, you may be able to clear the air hole with a thin, stiff wire or a long sewing needle. If this doesn't work, contact a radiator repair professional to assess the situation.

    Warning

    When you open the bleed valve, it may spit and sputter as air escapes, sending hot water flying in your direction. Take proper precautions and keep your face at a safe distance as you work.

  3. Secure the Bleed Valve

    You will know when all the air has been released from the boiler system because the bleed valve will start to release a steady stream of water. This is why you need to have a bucket in place before you begin, to avoid creating a mess on your floor. Use the radiator key to turn the bleed valve clockwise to tighten and secure it.

  4. Repeat the Process with Your Other Radiators

    After bleeding the radiator on the lowest floor that is furthest from the boiler, move to the next furthest radiator on the same floor and repeat this process to bleed the radiator.

    Continue moving sequentially closer to the boiler, then repeat this sequence on the upper floors until you have finished bleeding all radiators in the home. It's a good idea to complete this task about once every year to ensure your radiators are operating efficiently.

  5. Test the Heat

    After bleeding the radiators, check the boiler to make sure that it's working properly and the boiler pressure is normal. To check the pressure, look for the water pressure gauge on the front of the boiler.

    On a hydraulic gauge, you want the indicator needle to sit between 1 and 2. If it falls below 1, then there is not enough water pressure. If you have a digital gauge, there will be an alert or flashing reading to indicate if the water pressure is too low.

    If the water pressure in the boiler is too low, you will need to repressurize the system. A normal water pressure reading means that you can turn the heat back on and test the radiators to ensure they are producing heat.

FAQ
  • Do you bleed a radiator when the heat is on or off?

    You should always check to see that your central heating system or boiler is turned off and your radiator has completely cooled before attempting to bleed it. If left on, the radiator contains hot water, and you risk scalding yourself in the process.

  • How often do I need to bleed my radiators?

    It's recommended to bleed your radiators at least once a year, or maybe twice if you live in an area with an unusually long winter season. It's best to do it at the beginning of the heating season. This is an easy process that doesn't take much time, but it can significantly contribute to the efficiency of your heating system. By taking this step you ensure that they continue to operate optimally.

  • How do you know when the radiator is fully bled?

    Towards the end of the process, you will hear a hissing sound as trapped air escapes. This sound is followed by the trickle of water out of the bleed valve. This should turn into a steady stream of water and you can now close the bleed valve by turning the key clockwise.

  • Do I need a radiator key?

    If you don't have a radiator key, you can use a flathead screwdriver instead. It will fit into the notches of the bleed valve in the same fashion as a key. Turn counterclockwise to open the valve and clockwise to close it.

    Learn More: How to Use a Flat Head Screwdriver
  • How do I know if I have a water or steam radiator?

    To determine what type of heating system you have in your home, check the number of pipes connected to your radiator. One pipe indicates it is a steam system. Two pipes may indicate either a steam or hot water system. In a hot water system, there will be a second pipe used to return the condensed or cooled water back to the broiler.