Is the radiator warm at the bottom but cold at the top? There may be air trapped in the system. A radiator key allows you to open the bleed valve and release the air, helping the hot water circulate more easily throughout the radiator.
The shape provides a good grip and makes the key easy to turn, even when the valve is slightly stiff. The small hole allows you to attach it to a keyring or hang it somewhere easy to find.
The pack contains two radiator keys. Each key has an outer measurement of 9 mm and fits common square bleed valves measuring 5 × 5 mm.
- Switch off the heating or circulation pump and wait until the radiator is no longer very hot.
- Place a cloth beneath the valve and hold a small bowl or cup nearby. A little water may come out.
- Fit the radiator key onto the bleed valve. This is usually located at the top on the side of the radiator.
- Carefully turn the key slightly anticlockwise. Do not unscrew the valve completely.
- Leave the valve open while the air hisses out. Once a steady stream of water appears, the trapped air has normally been released.
- Carefully turn the key clockwise until the valve is closed. Do not overtighten it.
- Switch the heating back on and check after a while that the radiator is warming across the entire surface.
Good to know
The water released from the radiator may be hot. Open the valve carefully and protect the floor with a cloth.
If the radiator frequently needs bleeding, the valve leaks or the radiator still does not heat up, the heating system may need checking. In rented or managed accommodation, contact your landlord, building manager or managing agent.



















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