Electrical Electronic

How to bleed a radiator

Bleeding a radiator is the process of removing trapped air from your heating system. Allowing this air to escape will help you heat your home more efficiently and save money on your utility costs. It’s usually a clue that you need to bleed your radiator if you hear pipes slamming or radiators gurgling.

You may have turned up the heat in your house now that the temperature is falling, only to discover that one (or more) of your hot-water radiators is still chilly. If one of your radiators isn’t producing heat but the rest of your system appears to be working well, the issue could be air trapped inside the radiator, which is a regular problem with hot-water heating.

how to bleed a radiator

Before calling a plumber, try bleeding the radiator yourself to see if you can solve the problem. It only takes a few basic steps and requires very few tools. Take a chance! You’ll get the place nice and toasty in no time. Well, maybe that’s the reason you are here.

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In this article, the following questions will be answered:

  • When to bleed a radiator?
  • What are the things you need to bleed a radiator?
  • How to bleed a radiator?
  • How does air get into the hot water system?


When to bleed a radiator?

If your radiator is chilly on top but hot on the bottom, there’s probably air trapped inside, and you’ll need to bleed it. Well, here are some other indicators that your radiator needs to be bled:

  • The radiator is cold at the top
  • The entire system is cold
  • Mold and dampness caused by the system
  • Noise from the radiator


The radiator is cold at the top

This is the most common symptom that your radiator requires bleeding, which implies air has accumulated in the radiator, preventing hot water from circulating and heating it. Air must be released in order for your radiator to heat up properly. Patchy warmth in your radiator is a warning that it should be checked out before it quits heating up.

The entire system is cold

Though this isn’t as frequent as air trapped in radiators, it is certainly a symptom that your radiator requires maintenance. Because of trapped air in the pipes, the hot water that should be flowing into the radiator isn’t – this can lead to worse problems later if it isn’t fixed right enough! To get things warm again, you should contact your local heating engineer.

Mold and dampness caused by the system

If you’ve observed soiled wet patches or mildew on the walls, especially in rooms that aren’t used very often, it’s possible your radiators are in need of repair.

Noise from the radiator

Your radiators may create strange noises like gulping, gurgling, and rattling due to trapped air in your heating system. While this could be due to a variety of factors, it could also indicate that the radiator needs to be bled. In any case, your rad should be examined to ensure that the issue isn’t more serious.

Read more: Understanding an Air Conditioning System

Things you need to bleed a radiator

You’ll only need a few simple tools. Many bleed valves may be operated with simply a straight screwdriver. Ensure it’s the right size, though.

If you use a small screwdriver, the slot will wear out to the point where you won’t be able to move the screw, and you’ll have to call a plumber. A radiator key may be required for older radiators. These are available in a variety of sizes and can be found in old-fashioned hardware stores, home improvement stores, and plumbing supply houses.

How to bleed a radiator

To check and bleed your radiators, follow this simple step-by-step guide:

  • Turn on the heating system
  • Identify the radiator that needs bleeding
  • Turn off the heating and wait for the radiator to cold
  • Place a cloth below the radiator bleed valve
  • Open the valve and let the air escape
  • Close the valve
  • Check the boiler pressure


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Turn on the heating system

Turn on your heating and wait for all of your radiators to warm up (the length of time may depend on how many radiators you have and the size of your home, so be sure to give yourself plenty of time).

Identify the radiator that needs bleeding

Examine each radiator carefully to confirm that the temperature is consistent over the entire surface area. If you see any radiators that are cold at the top or hear any gurgling noises, this is a sign that there is trapped air inside and that you should bleed it.

Tip: When inspecting each radiator, we recommend wearing a thin pair of gloves because they can be quite hot.

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Turn off the heating and wait for the radiator to cold

We recommend turning off your heating before bleeding any radiators so that they aren’t too hot to touch.

Place a cloth below the radiator bleed valve

Locate the radiator bleed valve and place a cloth or an old towel beneath it to catch any water that may leak out. A bleed valve is located on every radiator. They appear like a circular hole with a square inside and are usually found near the top corner of a radiator.

Open the valve and let the air escape

When you bleed the radiator, if no water or air comes out, the valve could be clogged with paint. Close the inlet and output valves at each end of the radiator, then unscrew the bleed valve’s center screw. Slowly crank the radiator key anti-clockwise in the bleed valve (a quarter of a turn should be enough). As the air exits, you should hear a hissing sound.

Tip: Just in case you open the valve too much, keep a bucket nearby to catch any spitting water.

Close the valve

Turn the key clockwise to close the valve once the hissing stops and water start to leak out.

Check the boiler pressure

Repeat this procedure for each radiator in your home that needs to be bled. After you’ve completed this, check the pressure in your boiler’s water pressure gauge. You’ll need to re-pressurize the system if the boiler pressure is too low (below 1 bar). If the pressure is normal (between 1 and 2 bars), turn on your heater and make sure your radiators are heating up properly.

Read more: How to clean your home air conditioner

Watch the video below to learn how to bleed a radiator:

How air gets into the hot water system

What is the best way to get air into a closed plumbing system? In certain circumstances, it isn’t even air. Galvanic corrosion may be producing hydrogen gas if your pipes are made of a mix of iron and copper or brass. Alternatively, you could have an older pressure relief tank that relies on a pillow of air to keep harmful pressure from building up in the heating system. Cooler water dissolves some of the air, and the heat forces the gas out of the solution when the system is turned on.

A rubber bladder separates the water from the air in modern pressure tanks. Air can be sucked into old steam systems. The steam shrinks dramatically as it cools, creating a partial vacuum. Make sure an air eliminator is put right after the boiler to eliminate or reduce the buildup of air and other gasses in your system. This is a plumber’s work.

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Do you bleed your radiators with or without the heat on?

Because bleeding radiators with hot water flowing through the system increase the risk of scalds and burns, you should always do so after the heating has been turned off and the system has cooled down.

Which Radiators do you Bleed First?

If your property has more than two stores, start by bleeding the radiators on the ground floor, starting with the one farthest from your boiler.

How Often Should Your Radiators Be Bled?

At least once a year, hot water radiators should be bled. It’s always better to do this far ahead of the winter months so that your system is ready and in operating order when the weather starts to cool.

How Long Should A Radiator Bleed Take?

Bleeding in a radiator should take no more than 20 to 30 seconds on average. This varies depending on the radiator’s size and the amount of trapped air inside. Simply keep bleeding the radiator until the hissing stops and water starts to flow through the bleed valve. This indicates that the radiator has been bled off all air.

What is the best place to get a radiator bleed key?

Radiator keys are very easy to come by. They’ll be found in most hardware stores, and costs range from 50p to a fiver.