Radiator system

Over time air can seep into your central heating system and will tend to bubble up to the top of your radiators. This is especially the case radiators located on the top floor of your property. This trapped air can affect how efficiently the radiators heat up a room. Another sign is that they also get noisy when in use.

To check if you need to bleed your radiator, run your hands over it when the central heating is on. You may want to wear gloves and take caution when touching the radiator, being careful not to burn your hands.

If the radiator is cooler at the top than at the bottom, the chances are that some air has built up. Other symptoms may include gurgling noises or a radiator that takes longer than other radiators to warm up. In some cases, the radiator may even stay cold.

How to Bleed Your Radiators

Switch your central heating and hot water off at the boiler and wait for the radiators to cool down before bleeding them. This is extremely important as the water in the system will cool down and avoid any burns arising.

To release the air you will need a radiator key. This is small box spanner that fits the release valve in your radiator. If you don’t have this key, some radiators will allow you to use a flat head screwdriver.

To locate the release valve, check the top edge of your radiator and in the centre of this valve, there should be a small square pin.

Bleeding your radiator can be a messy job so to protect your paintwork and carpet, drape a cloth or towel between the radiator and the wall. You can also place a small bowl underneath the radiator to catch any water that might leak out.

Insert your radiator key into the valve and gently turn the release valve. Carefully twist it anti-clockwise the radiator will hiss as the air is slowly released. Water can also spray out of the radiator so be prepared. If the release valve accidentally comes out, use an adjustable spanner to replace.

Once all the air is released after a few seconds the hissing will be replaced by a spray of water. Keep the valve open and once a steady stream of water comes out, you will need to twist the key clockwise and close the valve.

Repeat this process on all of your radiators, starting with your radiators furthest away from your boiler, and then moving on to the radiators located upstairs.

Getting the Pressure Back Up

Boiler system

Once complete, inspect the pressure gauge on your boiler and check it is showing the normal recommended pressure level (usually around 1 to 1.5 bar).

If a lot of air was removed from the system, the overall heating system pressure can sometimes be too low to reach your furthest radiators. If this happens, use the filling loop (if you have a sealed system) on your boiler to fill it back up. It’s usually a tap or lever, however, each boiler is different so check your boilers manual to see how it is done.


To the best of our knowledge, the information contained herein is accurate and reliable as of the date of publication. Please see https://www.centralgassafety.co.uk/terms-of-use for more information.