How To Bleed A Radiator: A Step-by-Step Guide

Your home’s radiator needs regular maintenance to run as efficiently as possible.

Booking an annual service for your boiler is essential for maintaining its warranty and important for many other reasons. For this you must call in a professional.

However, there are some other jobs you can do yourself, and one of them is bleeding the radiators. You might ask why it’s necessary. Well, if your boiler is attached to a more extensive heating system, your radiators need to be bled to keep the system running properly.

While many DIY jobs are not recommended for homeowners to perform on their central heating system, bleeding your radiators is easy and safe for almost everyone to do.

But for those who have never bleed their radiators, what does it even mean?

What Does Bleeding Your Radiators Even Mean?

Bleeding your home’s radiators is a task that removes trapped air from your heating system. It may sound like an incredibly aggressive process, but we can promise you it isn’t.

Why must they be bled? Simply, because they have air in them.

Air can sneak into a closed heating system for several reasons, which include:

• Leaks in your system
• Air getting trapped during the initial installation
• Or general expansion and contraction of the system over time

Air accumulates in your home’s heating system and develops into air pockets. These air pockets can start to affect the efficiency of your boiler and lead to cold spots at the top of your radiator.

This is because air is a poor conductor of heat compared to water, which is 24.17 times faster.

Which is why one of the telltale signs that your radiator needs to be bled is when the air rises to the top and causes that cold spot.

Another sign that your radiator might need to be bled is if it is making a gurgling sound when your central heating is turned on.

Now that we know why and when you should bleed your radiators, what do you need to get the job done?

What Tools Do You Need To Bleed A Radiator?

While many DIY videos on the internet might require the homeowner to invest in a full set of tools, bleeding your radiator requires very few implements, and you probably already own them.

The items you’ll need are:

• Radiator key or a flat-head screwdriver
• Towel or cloth to protect your floor from potential spills
• And a small container to catch any water that escapes

Radiator keys are usually provided when the system is installed. If your radiator key has “grown legs,” you can purchase a new one from your local hardware shop.

But if your radiator is more modern, you can also use a flat-head screwdriver.

A good size for the small container to catch water would be one that can hold 200ml.

Now that we’ve gathered your tools, it’s time to take the steps to bleed your radiator.

Steps To Bleeding Your Radiator

Homeowners should bleed their radiators regularly, and it’s highly recommended that they do so before winter sets in. If this is a routine check, you’re just looking to ensure your heating is ready for the cold weather.

Step 1: Turn On Your Heating System

Turn on your heating system and set it at the highest setting.

Allow the system to reach temperature and feel if the radiators are heating evenly. Do not touch the radiator directly, and just pass your hand over it at a safe distance.

If you’ve been lucky and found no cold spots or heard no gurgling noises along your home’s heating system, you don’t need to bleed your radiator.

However, if you find a problem with a radiator, you should now turn off the heating system.

Allow the heating system to cool to room temperature before starting any work. Waiting periods can vary depending on the size of your system.

But while you’re waiting for the system to cool down, you can take the next step.

Step 2: Prepare The Area

Nothing will prolong a project more than searching for your tools. For this reason, you should prepare the space around the radiator you want to bleed.

While waiting for the radiator to cool down, place the towel at the radiator’s base and the water container nearby.

Step 3: Find The Bleed Valve

Most bleed valves will be located at the top of the radiator, and they can be on either side (left or right).

Usually, a bleed valve will look like a small metal square, or depending on the manufacturer and your opinion, it could look like a screw located with a hexagon nut surrounding it.

If you are in doubt, most radiator companies publish an online manual for their product for you to double-check.

Sometimes, valves on older radiators can be hidden under layers of paint or at the back of the unit (unlikely). But always do a thorough visual check before calling in an expert.

When you’re ready, it’s time for the next step.

Step 4: Bleeding The Radiator

Insert your radiator key, or use your flat-head screwdriver, and turn it in an anti-clockwise direction. Make sure to loosen the valve slowly, as a quarter rotation is often enough to release the trapped air.

When you hear a hissing sound, don’t panic, but make sure to have your container nearby to catch the water. As mentioned, you are trying to release trapped air in the system, and this hissing noise is caused by air escaping from your radiator.

Keep the valve in place or slightly open, and allow the hissing to end. Once the air has escaped, water will start to trickle out.

Do not open the valve all the way, as this will cause a significant drop in boiler pressure and a lot of unnecessary water to leak out.

Step 5: Watching For Water

As mentioned, water will trickle out of the slightly open valve when the hissing stops.

Depending on the size of the air pocket, water should start to trickle out between 20 and 30 seconds after opening.

However, with huge radiators, it can take a full minute. When the water trickling out of the radiator starts to flow properly, close the valve. Do not overtighten the valve, as it can cause issues in the future.

An example of an issue would be stripping the valve.

However, you want to ensure that the valve is closed enough to be watertight and that there are no leaks.

Step 6: Check Your System’s Water Level And Pressure

While you’re unlikely to drain the system, checking your system’s water level after bleeding is a good idea. If you’ve accidentally opened the valve too much or removed it completely, this step is essential.

Another check to perform is the system’s pressure. After you complete your work, your boiler’s pressure will drop slightly. Don’t turn the system back on yet. You want to make sure that when it is switched off (as it should be when bleeding your radiator), the pressure is between 1.0 and 1.5 bars.

When your heating system is operating, its pressure should be around 2.0 bars. If, at this point, you discover that your system’s pressure is too low, you can repressurise it.

Most boiler manufacturers’ manuals will have detailed steps for doing this safely.

But what if you identified more radiators with trapped air?

Step 7: Repeating The Steps

For those who completed their first round of radiator inspections and found multiple issues, you must repeat these steps for each unit.

If you have multiple radiators with cold spots, begin with the radiator furthest away from your boiler. In properties with two floors, bleed radiators on the ground floor first.

Check your system’s pressure after bleeding every radiator and, if necessary, correct it to the proper pressure.

But what if you still have issues with your radiators after following all the steps?

Call In An Expert

If you regularly need to bleed your radiators, this is a strong indication that your heating system has a leak or there’s a bigger problem with your boiler, which a Gas Safe registered engineer will need to fix.

Or, if you’ve bled all your radiators correctly and there are still cold spots at the bottom of your radiator, this is an indication that you have a build-up of sludge and will need a Gas Safe registered engineer to potentially perform a Powerflush.

If you’re ever unsure what to do next with your home’s central heating system, you can always talk to one of our consultants via the chat bubble in the bottom right hand corner.