Sometimes you may notice a cold patch at the top of your radiators, or they make a noise when they are warming up. This could be due to air that is collected at the top overtime and is quite normal. The air means that the hot water in the radiators can’t circulate as effectively so your home may take longer to warm up or rooms may never reach a desired temperature.

However, it is very easy to get rid of this air yourself making your heating system more energy-efficient and potentially saving money on energy bills.

Step by Step to bleed your radiators

  1. While your heating is on, carefully feel the tops of each radiator to check if they are warm. Those which are cold at the top need bleeding, if they have a cold spot at the bottom this could be an indication of system sludge and debris in the system and we will cover
  2. Switch off your central heating and let the radiators cool down before bleeding radiators.
  3. Starting with your downstairs radiators first, look at the valve on the top of the radiator, some need a screwdriver to undo them but most you’ll need a radiator key, these are widely available at DIY stores and online delivery stores.
  4. Holding a cloth underneath the valve to catch any drips, slowly turn the key anticlockwise to open the radiator valve. You should hear hissing as the air escapes. Do not fully remove the centre pin on this valve.
  5. When the hissing stops and the water starts to come out of the valve turn the radiator key clockwise to close the radiator valve. If the water is black in colour this is a sign off system sludge and debris, the system would need effective treatment to be cleaned thoroughly. This is also the case should the water colour be orange and the air being released smell very gassy (hydrogen), this is a sign of the system breaking down, water treatment is required again this will be covered in another top tip. Did you know 80% of system/boiler failures are due to poor system water quality.
  6. Repeat for all downstairs radiators before moving onto your upstairs ones.
  7. Knowing what type of heating system you have will help out, it will either be a pressurised system (topped up via a filling loop with a pressure gauge either located on the boiler or near to the filling loop. The pressure should read between 1 and 1.5bar, if it isn’t it needs topping up), or vented system (small header tank in your loft space which should naturally fill the system via gravity when air is released) water will need to be topped up.
  8. When you have checked that all the radiators are filled and no more air is escaping, turn on your central heating and that check that the radiators have not got any cold places at the top of them. If when on there are cold spots predominantly in the shape of a triangle at the bottom this is an indication your system has sludge and debris in it which is stopping it from working efficiently. This would require a powerflush and water treatment in the form of inhibitor added

We recommend you check your radiators at least once a year when you switch on your heating again after the summer. It is quite normal for a bit of air to have collected, especially in the radiator which is highest in your central heating system. This is often a heated towel rail in the bathroom and is easily overlooked so make a note to check this. If you see signs of rust or water when you check them or your radiators need bleeding more often than usual you may have a small system leak which will need fixing.