Start with the radiator furthest from the boiler and on the highest floor, then work your way back towards the boiler and downwards.

Where to start

  • Begin with the radiator that is furthest away from the boiler on the top floor, as this is where the most trapped air usually collects.
  • Then move radiator by radiator back toward the boiler, finishing with the closest radiator downstairs.

Basic bleeding steps

  • Turn the heating and boiler off and let the system cool before you start.
  • Use a radiator key or flathead screwdriver on the bleed valve, with a cloth or container underneath to catch any drips.
  • Turn the valve slowly anticlockwise until air hisses out, then close it as soon as a steady stream of water appears.
  • When all radiators are done, check boiler pressure (often around 1–1.5 bar when cold) and top up if needed, then turn the heating back on.

Quick safety notes

  • Never bleed radiators while the boiler is running or the system is very hot, to avoid scalding water.
  • If you keep needing to bleed radiators or the pressure drops repeatedly, a heating engineer should check for deeper system issues.

Information gathered from public forums or data available on the internet and portrayed here.