Radiator cold at the top, warm at the bottom
Air in the radiator. Bleeding it is a genuinely easy DIY job: five minutes, one small key.
What it actually means
Air rises, so trapped air collects at the top of a radiator and stops hot water filling that space. The bottom heats, the top stays cold.
This is the single most DIY-able heating fault there is. No tradesperson needed, just a radiator key from any DIY shop (or often a flat screwdriver on modern valves).
Try this first, before you spend a penny
- 1
Turn the heating off
Let the radiators cool so the air collects and you do not get sprayed with hot water.
- 2
Open the bleed valve slowly
Top corner of the radiator. Quarter turn with the key until you hear hissing. Hold a cloth under it.
- 3
Close when water appears
A steady dribble of water means the air is out. Nip it closed.
- 4
Check the boiler pressure after
Bleeding drops system pressure slightly. Top back up to about 1.2 bar if needed.
When it is a pro job
If radiators need bleeding every few weeks, air is getting in somewhere, which usually means a small leak or a system fault worth an engineer's look.
Heating engineer or plumber
DIY is free. If you would rather someone did it, a plumber will bleed and balance the whole system for well under three figures in most of the UK.
£0 to £100
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