How to bleed a radiator

Why do I need to bleed my radiator?

Bleeding your radiator is a routine part of radiator maintenance. As water fills your radiator, overtime small amounts of air will creep in and eventually mean that your radiator will not function properly. As the air builds up in the radiator it leaves less and less room for the hot water to heat the radiator meaning they become inefficient and costing you far more on your heating bills in the long run.

How can I tell if my radiator needs bleeding?

It’s quite simple to find out whether your radiator needs bleeding. All you have to do is make sure your heating is on and then feel the bottom and the top of the radiator. If the top feels cold while the bottom is warm then you will need to bleed your radiator as the air is stopping the hot water reach up into the radiator.

So how do I bleed a radiator?

  1. Step 1: Bleeding a radiator is easy and once you know how to do it you’ll be able to make sure your radiator is functioning at maximum efficiency all the time. First of all you will need to locate your radiator’s bleeding valve. This is usually at the top side of a radiator.
  2. Step 2: Secondly, get yourself a towel and a container, like a washing up bowl, to place under the valve on your radiator. These will come in useful when the radiator is bled as water will some time dribble out of the valve. 
  3. Step 3: Before bleeding your radiator make sure you turn your central heating off and leave the radiator to cool for about 20 minutes. This is very important as the water inside radiators can be scolding hot and may be so for a long time after the heating is turned off.
  4. Step 4: After you have located the valve, left the radiator to cool and have a means of catching the water, use the valve key provided with the radiator and place it into the slot on the valve.
  5. Step 5: Turn anti-clockwise slowly until you hear air coming out with a hissing noise. Do not turn the valve any further and let the air come out, the towel placed underneath, until water begins to come out of the valve.
  6. Step 6: When this happens tighten the valve immediately clockwise. Check the pressure on the gauge on your boiler and, if it is below normal, top it up using the lever on the boiler known as the external filling loop.
  7. Step 7: Turn the taps slowly, for safe water control, until the pressure is restored. Once this is done or if you didn’t need to restore the pressure, turn your central heating back on and check your radiator again for cold spots. If the whole radiator is warm then the problem id fixed and radiator is functioning at maximum efficiency again.

What if I don’t have a valve key?

If you don’t have a valve key then it is quite easy to get hold of one from your local DIY store. Valve keys come in different sizes so be sure to match it to the slot on your radiator’s bleeding valve. You can also buy multi-keys if you are unsure which one will fit your valve.

Failing that, there are other methods of loosening the bleeding valve. If your radiator bleeding valve has a slotted indentation then a slotted screwdriver will do the job, however it has far less control than a valve key. Pliers or a wrench can also be used however be very careful if you do so as their grip can wear down the valve if applied too vigorously.

Alternatively an Allen key, or hex key, may be able to fit into a bleeding valve with a matching size/patterned slot.

What if the bleed valve is worn or damaged?

If the bleed valve is worn or damaged, you may still be able to unscrew it with a wrench or a pair of pliers. However, it is best to replace the damaged valve all together rather than risk further damage to your radiator.

To replace a bleeding valve, first check the normal pressure of your boiler and note it down. Turn off the central heating allowing the radiator to cool right down before working on it and also close any valves on your radiator. When the radiator is cool, you will have to undo the outer fitting of the valve with a large spanner or wrench. There will be some spillage so prepare a bowl and a towel underneath the valve as above. 

Once the outer fitting is loosened, take out the inner fitting of the damaged valve and replace with a new one which can be bought at any DIY store. Tighten the outer fitting and then bleed your radiator as instructed above and then afterwards check the boiler pressure, adjusting it if necessary.

If your radiator has a bleeding valve set into it or the inner fitting of the valve will not come out then you will have to purchase a new radiator.

What if my radiator does not have a bleeding valve?

Whilst this is unusual, some older radiators do not have a bleeding valve. If this is the case, you can still bleed the radiator but this will have to be done at the boiler instead. As with bleeding a radiator, turn the heating off and let the system cool for about 20 or 30 minutes. One the system has cooled down, find a towel and a bowl to place under the boiler valve.

The boiler valve should be beside the boiler and be connected to two pipes. Using either the valve key that came with the boiler or a screw driver, carefully loosen the valve as with the radiator, allowing the air to hiss out. When water begins to come out of the valve, tighten it straight away, and check the pressure as above.