Air can become trapped in your central heating system. This is known as an air lock. Common causes of air in the central heating system are incorrect refilling or by air being drawn in at some point.

To solve this problem you’ll need to bleed the radiators. You’ll need to do this in the correct order.

  1. Switch the boiler off and isolate the electrics.  This is very important.
  2. Turn off the lockshield valves (usually covered by a cap). Turn these anti-clockwise to open. Make a note of the number of turns required.
  3. If you’re working across two or more levels, start at the bottom (ground floor) and work your way up.  Start at the first rad on the circuit.
  4. Open the flow valve.
  5. The bleed valve (usually at the top right) can now be slowly opened using a bleed key.  As soon as water escapes the radiator has been bled and is free of air.
  6. Open the locksheild valve by the same number of turns used to close it.
  7. Repeat for the remaining radiators in the system.
  8. Once complete, you can turn the system back on, making sure to check the pressure, topping up with water (unvented system) if required.

Further reading: more information on bleeding radiators

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