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How to bleed your radiator

Bleeding your radiator every so often could potentially save you energy and improve your heating performance.

Radiator bleeding is the process of letting any trapped air escape from your home’s heating system. This will increase heating performance, energy efficiency and get rid of those rattling sounds which will ultimately save you money on your heating bill.

When do I need to bleed my radiators?

To assess whether you need to bleed a radiator or not, start by turning on your heating system and allowing it to start warming up your radiators. While they’re warming up, listen for any clanking or rumbling sounds - this could be pockets of air rushing through your heating system.

The second indicator to determine if your radiators require bleeding is to feel the top of the radiator to see if it has heated up. If it’s cold at the top and hot at the bottom, there’s likely to be a build-up of air in the system. Again, please take extra care here as the radiators will be hot, so be sure to use gloves.

We recommend regularly checking your radiators and bleeding them as necessary however a rule of thumb is bleeding them every year.

If you have to repeatedly bleed radiators, then discuss this with your installer when the boiler is serviced as there may be an underlying problem.

We have a create a 7-step guide to bleed your radiator

The tools needed to bleed the radiator:

  • A radiator key to open the bleeding valves of your radiators. This is used to open the radiator vent valve. These are purchasable from hardware stores or from online retailers.
  • A bucket & cloth. Your radiator will leak water when the air has fully escaped, so you will want to catch it before it wets your floor.
  • A pair of gloves. These will help protect your hands from any hot pipes or surfaces.

Make sure your central heating system is turned off. This will stop your circulation pump from operating and moving heating water and air through your pipes, cooling down your radiators and making them safe to bleed. All thermostat valves need to be open.

After switching off your heating, wait approximately 1 hour (or 2 hours to be cautious) to ensure that all radiators are cold. This prevents you from getting burned in case hot water or steam leaks during the bleeding process.

This is where you’ll begin to bleed the radiator. First, locate the radiator valve, which can usually be found at the upper side of the radiator - different models will have it located in different places, however. For reference, it looks like a small, round hole with a little square inside.

Prepare the area by placing the bucket beneath the valve and keep your cloth pressed against the wall to protect from spraying water.

Slowly turn the radiator key anti-clockwise. A quarter to half a turn should be sufficient to open the valve enough for air to escape. You will hear a hissing noise as soon as air drops out of the radiator - that’s how you know you’re bleeding the radiator correctly. Do not continue opening the valve once you hear a hiss or you will risk leaking excess water out of your radiator.

Once the hissing stops and only water is exiting the valve, you have successfully bled that radiator and can close the valve. Do note that water can sometimes be discoloured from time spent in the system, this is not a cause for alarm.

Before closing the valve, be sure to let a small amount of water run out before you turn the radiator key clockwise to close the valve. This ensures you’ve gotten rid of all trapped air in that radiator. Don't close the valve too tight, otherwise you might damage it.

You’ll want to bleed all the radiators that are affected by trapped air, though it doesn’t hurt to simply bleed every radiator and ensure there is absolutely no air left in the system. It’s easy to check by opening the valve and checking for the hiss - if it doesn’t hiss, you know your radiator is good to go.

Air will naturally rise as it is lighter than water, so bleed all radiators in the ground floor before heading upstairs if you have a multi-story property. This will ensure best results and save you time having to go back and forth.

Before you switch your heating back on, be sure to check the water pressure of the system by looking at the pressure gauge or digital display on the boiler - you may get an F22 fault code (please refer to the operating instructions for guidance if you are unsure). The boiler should read between 1 to 1.5 bar of pressure when the central heating is cold.

If the pressure is too low, you need to refill the heating water. If you are unsure how to refill your boiler, watch our video on pressurising your gas boiler here.

Finally, check if all radiators are warming up evenly and noises have been reduced. That’s all there is to it! Do be sure to bleed your radiators regularly to ensure the best heating performance.

Is your heating system still not working properly?

Contact an installer if your heating system keeps showing problems.