How to bleed your radiators — and why it cuts your heating bill
Trapped air in radiators forces your boiler to work harder. Bleeding them takes five minutes and can reduce your bills by 5–10%.
If your radiators are warm at the bottom but cold at the top, there's trapped air in the system. Bleeding them is one of the simplest things you can do to improve your heating efficiency.
What you need
- A radiator bleed key (available at any hardware shop for under £2)
- A cloth or small bowl
Step-by-step
1. Turn your heating on and let the system fully heat up
2. Feel each radiator — cold spots at the top indicate trapped air
3. Turn your heating off and let the system cool for 30 minutes (important — hot water under pressure can cause burns)
4. Insert the bleed key into the bleed valve (usually at the top corner of the radiator)
5. Turn anti-clockwise — you'll hear a hissing sound as air escapes
6. As soon as water starts to trickle out, close the valve clockwise
7. Repeat for each affected radiator
After bleeding
Check your boiler pressure gauge. It may have dropped slightly — if it reads below 1 bar, you'll need to repressurise using the filling loop (your boiler manual has instructions, or call a Gas Safe engineer).
How much can you save?
The Energy Saving Trust estimates that inefficient radiators can add 5–10% to your heating bills. On a £1,200 annual gas bill, that's £60–£120 in wasted money. Bleed your radiators at the start of each heating season.