Last updated: March 2024

Keeping all your radiators in optimal condition takes just a few minutes of your time, but it could reduce your energy bills by over £90 per year.¹

In this guide, we’ll explain how to bleed your radiators and everything else you need to know about keeping your radiators in tip top condition.

What is radiator bleeding?

Radiator bleeding is a simple but important maintenance task that ensures your heating system runs efficiently.

Over time, air can get trapped inside your radiators and prevent hot water from circulating properly. This can prevent your radiator from heating up evenly, either resulting in a colder room or your boiler working harder (using more energy) to bring the room up to the desired temperature.

Bleeding your radiators removes this trapped air, allowing hot water to flow around the radiator easily and evenly. It’s an essential task for keeping your home energy efficient.

Signs a radiator needs bleeding

If your radiators have air trapped in them, they might show some of the following signs:

• Cold spots: If you notice cold areas (especially at the top) of an otherwise warm radiator, this is a classic sign that air’s trapped in the system. The cold spots occur when trapped air stops hot water from flowing evenly around the radiator.
• Gurgling noises: When you turn on the heating, listen for any unusual sounds coming from your radiators. Bubbling or gurgling noises can indicate that air is trapped inside, disrupting the flow of water.
• Takes longer to heat up: If your radiators are taking longer than usual to heat up, it could be due to air pockets reducing the efficiency of your heating system.
• Increased heating bills: Trapped air can make your heating system work harder to heat your home, leading to higher than usual energy bills.
• Cold radiator but hot pipes: If the pipes leading to the radiator are hot but the radiator itself is cold, this is a strong indicator that air inside is preventing the hot water from circulating properly.

Recognising these signs early and bleeding your radiators accordingly can help ensure that your heating system is working efficiently, keeping energy use and bills to a minimum.

Tools you’ll need to bleed a radiator

You don’t need many tools to bleed a radiator. But beware! It can be a messy job, so consider all the options on this list:

• Radiator key: This small, simple tool is designed specifically for bleeding radiators. It fits into the bleed valve found on the side or top of your radiator. You can buy them from most hardware stores and large online retailers for just a few pounds.
• Cloth: Bleeding a radiator can sometimes release water along with the trapped air. A cloth can help catch any drips and protect your floor and walls.
• Tray/container: Sometimes a radiator will release more water than a cloth can absorb while it’s being bled. So it’s wise to place a tray or small container underneath the bleed valve.
• Gloves: To protect your hands from potentially dirty or hot water, consider wearing gloves you don’t mind getting dirty.

These tools will make your life a lot easier when bleeding your radiators.

How to bleed a radiator

Bleeding a radiator is a simple process that can usually be done in less than a minute:

1. Turn off your heating system: This prevents more air from being drawn into the system and reduces the risk of hot water splashing you when you bleed the radiator.
2. Locate the bleed valve: The bleed valve’s typically on the top side of the radiator. It’s a small valve that has a square-looking notch that matches the shape of the radiator key. ‍
3. Prepare the area: Place a tray or container under the bleed valve to catch any drips. And hold a cloth around the valve itself to catch any upward or side spray. ‍
4. Bleed the radiator: Fit the radiator key into the valve. Gently turn the radiator key anti-clockwise to slowly open the valve. You might hear a hissing sound as the trapped air escapes. Hold the key steady until the hissing stops. When a small amount of water starts to leak out, the air should be fully released. Close the valve firmly but not overtight as this can damage the valve. ‍
5. Turn the heating back on: Check the radiators to make sure they’re heating up evenly without cold spots. ‍
6. Repeat if necessary: If you notice that a radiator still has cold spots after the heating’s been on for a while, you may need to repeat the bleeding process to release any remaining air.

It may take a few minutes to get right the first time. But with a bit of practice, you should be able to bleed a radiator in less than a minute.

What if a radiator still has symptoms after bleeding?

If your radiator still has cold spots or other issues, you might want to check the following:

• Did you bleed it fully? Sometimes air can be left behind. If a radiator is still cold after bleeding, or it’s not heating up properly after bleeding, try bleeding it again before investigating other options.
• Is the boiler pressure too low? Bleeding the radiators lowers the pressure in your central heating system. If it becomes too low, it will need re-pressurising. Check your boiler manual for instructions on how to do this.
• Are the radiators balanced? If a radiator is heating up slower than others, your system might need balancing. This simply involves adjusting the valves on each radiator to make sure hot water is evenly distributed throughout your home. Read our guide on how to balance radiators yourself.
• Is there a build-up of grime? Radiators can accumulate sludge and debris over time, which can slow or block the flow of water. If the radiator still doesn’t heat up properly after bleeding, you might need to hire a professional to flush the system.
• Is the radiator thermostat valve faulty? A malfunctioning thermostat can prevent the radiator from heating up efficiently. If there's an issue, it’s best to speak with an expert to diagnose and fix it.

Why should you bleed your radiators?

Bleeding your radiators can improve your home’s energy efficiency, reduce your bills and result in many other improvements:

• Improves energy efficiency: Trapped air in your radiator can prevent hot water from circulating properly. By bleeding your radiators and removing this air, you allow the entire system to heat up more efficiently, which can lead to significant energy savings.
• Ensures even heating: Air that’s trapped in a radiator can cause cold spots, which can result in one area of a home being cooler than another when the heating’s on. Bleeding your radiators removes this air, ensuring that heat is distributed evenly throughout your home.
• Reduces heating costs: Improved efficiency means your heating system won’t have to work as hard to maintain your desired temperature. This can lead to lower heating bills, since your system will use less energy to get your home up to temperature.
• Extends boiler lifespan: Bleeding your radiators can help prevent issues that strain your boiler, such as reduced efficiency and premature wear.
• Increases comfort: Eliminating cold spots and ensuring even distribution of heat throughout your home will make your home more comfortable to live in, particularly during the winter.
• Detects other issues: Bleeding your radiators could help identify other issues within your heating system, such as a malfunctioning radiator or problems with the boiler pressure.

When should you bleed your radiators?

There’s no single best time to bleed radiators. But there are two ways to decide when to bleed your heating system:

• Annually: It’s good practice to bleed your radiators every year to prevent issues from occurring. Autumn would be a good time, since you’ll be using your radiators more in the colder months and will want them working optimally.
• When you notice an issue: If you notice any signs of air trapped in the system, it’s best to address it straight away since leaving it could lead to bigger problems. Signs include cold spots at the top of the radiator, gurgling noises or radiators that take longer than usual to heat up. See our section Signs a radiator needs bleeding for a full list of what to look out for.

FAQs

How long does it take to bleed a radiator?

It should take less than a minute to bleed a radiator. You’ll need a radiator key, a cloth and a tray to capture any drips.

Which types of radiators need bleeding?

Most types of radiators need bleeding from time to time, including:

• Panel radiators: These are the most common type of radiator used in homes. They’re made of flat or corrugated panels that are filled with water.
• Column radiators: Made up of vertical or horizontal columns, these work in the same way as panel radiators.
• Convector radiators: Convector radiators are more efficient than panel radiators thanks to a convector fin that sits between panels.
• Cast iron radiators: You may need to bleed a cast iron radiator more often than more modern types of radiators due to the way they circulate water.
• Towel rails: You’ll need to bleed a towel radiator every now and again, particularly if it’s used infrequently.

Can bleeding radiators improve EPC?

Bleeding your radiators may improve your EPC (Energy Performance Certificate) rating, but it’s likely to be a very small improvement. It can improve the efficiency of your central heating system, heat your home more evenly and reduce strain on the boiler. But these improvements are less impactful to your home’s energy efficiency than larger improvements such as improving insulation, upgrading your boiler, installing double glazing or fitting solar panels.

How much energy can bleeding a radiator save?

The exact amount of energy savings from bleeding a radiator will vary depending on a variety of factors, including the size of your home, the efficiency of your heating system and how much air was trapped in your radiators before bleeding.

But the principle is straightforward: bleeding radiators can improve the efficiency of your heating system by allowing hot water to circulate more effectively, which in turn can reduce energy consumption.

If all your radiators were half filled with air, your boiler would need to operate for a longer period or at a higher temperature to achieve the same level of heating.

Can you bleed a radiator yourself?

Typically, yes. Most people should be able to bleed a radiator themselves. It’s a simple task that just requires having a radiator key and a cloth or tray to catch any drips.

What is a radiator bleed key?

A radiator bleed key is small tool that unlocks the air vent valve of a water-filled radiator. This lets air escape, allowing the radiator to operate more efficiently. There are different types of radiator keys, so make sure you get the right radiator bleed valve key. You should be able to buy them for around £1.

‍Find out how to make your home more energy efficient with our free energy efficiency plan.