BoilerMaintenance2025-10-06
How to Bleed Radiators (and Why)
Radiators warm at the bottom but cold at the top usually just need bleeding to release trapped air.
Bleeding radiators is a simple task that restores even heat and efficiency when air gets trapped in your heating system.
When to bleed
If a radiator is warm at the bottom but cold at the top, trapped air is the cause. Bleeding releases that air so hot water can fill the whole radiator again.
How to do it safely
With the heating off and cool, use a radiator key on the bleed valve, release the hiss of air until water appears, then close it. Re-check boiler pressure afterward and top up if needed.
Key takeaways
- Cold tops mean trapped air — bleed it
- Turn heating off and let radiators cool first
- Have a cloth ready for drips
- Check boiler pressure after bleeding
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