How to Bleed a Radiator

To ensure effective performance of a water-filled radiator, you need to make sure that the radiator has been "bled" properly.  Bleeding a radiator means getting rid of any air that has accumulated at the top of radiator. When air is present, there is no water, which means no heat. Bleeding a radiator is done by opening an “air vent” otherwise known as a “bleed valve”.  Ideally radiators should be checked for air accumulation at least once a year.

To bleed a radiator you will usually require an appropriate tool, namely a flat headed screwdriver, a “bleed key” or a spanner.  Bleed keys (vent keys) are not included as standard but can be purchased from a plumbers' merchant or home improvement store. 

Bleeding a radiator is a simple process:

1.    Ensure both valves at the bottom of the radiator are open;

2.    Get a bleed key (vent key), screwdriver or spanner ready to open the bleed valve (air vent) at the top of the radiator.  Have a rag or cloth ready to catch minor drips;

3.    Use the tool to open the air vent and release the air holding the cloth underneath;

4.    Listen for the change in sound; you will hear a hissing noise at first, which is the sound of air escaping.  Vent the radiator until the sound changes and you get a steady stream of water.  At this point you can retighten the air vent using the tool.

5.    Once you have bled the radiator, turn the heating back on and leave the system to flow for half an hour.

Please note: On first filling a system, it is air that is vented from a radiator. However, from then on the periodic venting required is actually releasing hydrogen that is the by-product of rusting in the system.  If regular bleeding is continually required, then this is a strong indication that the system requires draining, cleaning and refilling incorporating a corrosion inhibitor to prevent further rust in accordance with BS5449 section five commissioning.  Alternatively, if regular bleeding is required then this could indicate a leak that is letting air enter the system.

Alternatively modern radiators do sometimes come with “automatic bleed vents” which release air from a radiator whenever necessary, meaning that you do not need to bleed the radiator manually.  These are great for convenience, however there are instances of automatic bleed vents causing damage to a radiator as regular venting can mean regular water seepage which can lead to corrosion.    

For more advice on maintaining your radiators, contact a radiator specialist such as Feature Radiators; their expert team can provide technical help on a variety of radiator related subjects.  Contact them on 01274 567789, view their website http://www.featureradiators.co.uk or visit them in person at their showroom at The Old Post Office, 134-140 Main Street, Bingley, West Yorkshire. BD16 2HL