What Causes Air In Central Heating Radiators And How To Fix It


If your central heating radiators aren’t heating up as they should be or you hear bubbling noises, chances are there is a build-up of air inside them. When this happens the radiators are less efficient, which isn’t ideal, particularly in the winter months.

Air caught up in central heating radiators occurs more often than people might think but there is no need to worry because this problem can be easily fixed. Before providing the solution to the issue, here are a few reasons why air builds up in central heating radiators.


Why Air Builds Up In Central Heating Radiators 

  • Air can build up in radiators as a result of installing the pump above the supply tank.
  • There can be an accumulation of hydrogen in the system as a result of rust within piping or the development of too much sludge.
  • Leaks are often a cause for air build-up. This can happen if you frequently re-pressurise the boiler.


How To Fix The Air Build-Up Problem  

If you have air trapped in your radiators you need to bleed your heating system. It will quickly have your radiators functioning as they should again and save a lot of energy and money in the process. 


The Tools Required To Bleed Your Radiators 

Before you get to work make sure you have the following items at hand:

  • A screwdriver or radiator bleed key (these can be found at most DIY stores).
  • A small container to collect the spillage of fluids.
  • A large towel to keep the surface area dry and avoid accidents.


Step-by-step Instructions To Bleed Your Central Heating Radiators 

Follow the simple steps below to check and bleed your central heating radiators:

  1.     Turn your central heating to its maximum heat setting and let your radiators run at their highest temperature for a minimum of 15 minutes.
  2.     At this point switch off your central heating system completely to stop air being pumped around. Thereafter, give it another 15 minutes to cool down.
  3.     Go to the radiator nearest to the boiler and turn off the radiator valve. After that, put a container underneath the bleed valve.
  4.     With a large towel in hand, use your screwdriver or bleed key to turn the valve anti-clockwise until water rather than air comes out (you’ll initially hear a hissing sound, which will be the air escaping and then water will start to come out). Be very careful not to turn the valve all the way when you’re opening it, as it can be very difficult to close again from that point.
  5.     When there’s no more water coming out, re-fasten the bleed valve.
  6.     Got to all your other radiators and repeat steps 3 – 5. Start with the radiators nearest to the boiler and work your way around the property.
  7.     When step 6 is complete, switch your central heating system back on again.
  8.     Double-check that the water pressure inside the boiler is between 1.5 and 2 bar (within the green section of the gauge). If the pressure is too low you just need to rebalance it by topping up the boiler.


Once you’ve completed the 8 simple steps above your central heating radiators will be free from air build-up and back to functioning as they should be.