In this guide we’ll show you how to bleed a radiator in eight easy steps; increasing the efficiency of your central heating, cutting your energy bills and making your home warm during the cold seasons.
Bleeding a radiator (also sometimes called bleeding a boiler) means letting out air that has become trapped inside your system, it's a common issue in un-vented heating systems. Trapped air prevents water from heating your whole radiator, creating cold spots. Sometimes you will hear a flowing or clucking sound coming from your radiator, this is also a good indicator that you need to bleed your boiler system.
If you touch the top section of your radiator, does it feel cooler than the bottom half? This means your heating system is working inefficiently. As your boiler works with your radiators, you’re paying for heating but not enjoying the benefits.
Fortunately, you can easily bleed your radiators yourself, making your home cosy and warm.
If you’re looking to bleed air from radiator systems you’ll need the following tools:
Venting heating systems is straightforward, just follow the steps below:
Before bleeding, you first need to turn the heating on so that all the radiators warm up. This builds pressure in your radiator that will push the unwanted air out.
Go through your whole house checking each radiator for cold spots.
Remember: The radiators will be hot, so take extra care with this step. We advise wearing a pair of thin gloves so you do not burn yourself.
What are the signs that the radiator needs bleeding? If you can hear gurgling sounds, the radiator takes a long time to heat up or there are cold spots then it is likely there is trapped air. This is preventing the hot water from filling the radiator; you will need to bleed that radiator.
Do not forget: You need to switch off your central heating before you bleed a radiator. If your heating is on you’ll risk scalding yourself and covering the floor with water.
Water may be discoloured when bleeding an old radiator, by putting old towels down you can save a cleaning job later, especially if you have light carpets!
Take the radiator bleed key, you’ll need to insert this into the bleed valve. Often the bleed valve (or nipple) is found at the top of the radiator, to the side. It looks like a round hole with a square inside. When you insert the radiator key into the bleed valve, you will feel them lock together.
Tip: If you do not have a radiator vent key it is sometimes possible to use a flat-headed screwdriver on modern radiators.
Carefully turn the valve anti-clockwise – as the air begins to escape you’ll hear a hissing sound. Be careful, the escaping air could be hot, keep sufficient distance.
A quarter to half a turn will be enough, never open the valve fully because once you bleed air from the radiator water will come rushing out.
Continue this process, holding the radiator bleed key until the air stops coming out. When only water is dripping from your radiator, then you have completed the bleeding process. Turning the bleed valve clockwise will seal the radiator; take care not to over tighten.
Modern bleed valves may release water as a ‘jet’. Turn your bleed valve key with care, and be prepared to quickly close the bleed valve.
You will need to bleed all the radiators in your property. We suggest starting on the ground floor and working your way up your property because the air rises through the system.
Once you have completed the task of bleeding all your radiators, you will need to re-pressurise your heating system. When you bleed a boiler heating system you always lose some water. If it’s a large amount then your system may have difficulty heating the top floors of your property or the central heating system can fail entirely.
If the water pressure in your system is correct, the needle gauge on your boiler will be facing green. If it’s on yellow then you will need to re-pressurise the system. To do this you’ll need to locate the central filling loop connected to your boiler. It looks like a tap and is connected to your main water supply; for reference, the pressure in a typical family home is usually between 1.0 and 1.5 bar.
Always turn the tap and slowly adjust the pressure. In the unlikely event that you add too much pressure and the needle faces the red, there is also a bleed tap.
You can find more information on that topic in our article about boilers losing pressure.
We advise bleeding your radiators at the beginning of the heating season, before you really need it. Making sure your boiler and heating system is running at its best without any trapped air before you need it.
Experts recommend not turning temperatures too high, this can save you a lot of money when the heating bill comes in. Hallways, kitchens and storage rooms are often comfortable at around 16 to 18°C, and living rooms feel warm at around 20°C.
Bathrooms and children’s rooms are often slightly higher at around 23 to 24°C.