How to Bleed a Radiator in Mere Minutes

This is a rare instance where bleeding is actually a good thing

Conroy Baltimore
Written by Conroy Baltimore
Updated May 13, 2022
A woman reading a book
Photo: d3sign / Moment / Getty Images


Simple project; big impact.

Time to complete

15 minutes

10 to 15 minutes, depending on the number of radiators in your home

Need professional help with your project?
Get quotes from top-rated pros.

What you'll need:


  • Bleed key
  • Flathead screwdriver


  • Protective gloves
  • Small bucket or bowl
  • Towel or rag

Picture this: you’ve come inside after a long day of battling frosty weather; all you want to do is crank up the heat, get in comfy clothing, and grab a warm beverage. After turning on the heat, you hear a weird knocking noise coming from your radiators and notice they aren’t heating properly. 

Unfortunately, some air is trapped inside, disrupting the hot water circulation. By learning how to bleed a radiator, you’ll get your system back to its standard functionality in no time.

How to Bleed a Radiator in 5 Steps

  1. Turn on the Heat and Identify the Problem Radiators

    First, turn on your central heating and wait for the radiators to warm up. The waiting period depends on your home’s size and the number of radiators present. 

    Once you think your house is warm enough, walk around and check if heat is coming from each radiator. Don’t touch them directly because you could burn yourself. Instead, put on protective gloves and run your hand along the top to feel for heat. If there are any cold spots, you need to bleed the radiator.

    Here are a few signs you need to bleed the radiator:

    1. The radiators aren't heating up properly 

    2. The radiators are cold at the top and warm at the bottom

    3. The radiator is noisy (knocking, hissing, or banging)

    4. The radiator has mold growth near the unit or the boiler

  2. Turn the Heat Off

    A man turning the heat off
    Photo: zoranm / E+ / Getty Images

    After identifying the problem radiators, turn off your heat. To avoid injury, give them some time to cool off before bleeding. The last thing you want is boiling water bursting from your pipes as you begin releasing air.

  3. Open the Radiator Bleed Valve

    Using the protective gloves, confirm the radiators have cooled off enough. If so, it’s time for bleeding (we promise it’s not as menacing as it sounds).

    Place a towel or small bucket underneath the radiator to catch any dripping water. Next, locate the radiator bleed valve—it’s usually located near the top of the radiator and looks like a round hole with a square inside.

    Use the bleed key or flathead screwdriver and open the valve by turning it slightly counter-clockwise. The escaping air will make a hissing noise, and water will trickle out.

  4. Close the Valve and Repeat

    A woman fixing and bleeding air from central heating
    Photo: m-gucci / iStock / Getty Images Plus / Getty Images

    You’ve successfully bled a radiator once the air stops hissing and there’s a steady trickle of water. Close the bleed valve by turning the bleed key or flathead screwdriver clockwise. (However, proceed with caution here. Closing the valve too tightly could damage it, and replacing a radiator valve costs between $150 and $300.)

    Wipe away any excess water to avoid rust on the radiator. Then repeat the steps with other problem radiators.

  5. Check Your Boiler Pressure

    After bleeding all of the radiators in your home, check the boiler pressure gauge. It should be in its usual position, between 1 and 2 bars. 

    If bleeding doesn’t fix the problem, you might have to replace a radiator, and costs range between $250 and $2,500. Before making any decisions, contact a local HVAC specialist to inspect your system and diagnose the issue.

Bleeding a Radiator Yourself vs. Hiring a Pro

Bleeding a radiator yourself is simple DIY. You don’t need to hire a professional unless you can’t allocate time to complete the project. It costs $1 to $2 to buy a bleed key to open the valves, whereas hiring a pro to bleed a radiator costs $100 to $200.

FAQs About Bleeding a Radiator

How often should you bleed radiators?

You should bleed your radiators at least once a year. Try completing this task before the colder months to avoid problems with your system as temperatures begin dropping.

Where can you buy a radiator bleed key?

You can find a radiator bleed key in most home improvement stores. They cost about $1 to $2.

Which radiators should you bleed first?

If your home has two stories, start with radiators on the first floor. Otherwise, bleed the radiator that’s furthest away from your boiler.

Need professional help with your project?
Get quotes from top-rated pros.