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What is a bleed key?

What is a bleed key?

Shop for Radiator Keys

The parts of a bleed key

Bleed key  The parts of a bleed key are:

  • The handle
  • The shaft
  • The square socket that fits over the square-headed bleed screw
Clock key radiator bleed keys Bleed keys are used for ‘bleeding’, which is the release of air from radiators via the air vent plug. Air trapped in a radiator can drastically reduce its efficiency.

They are known as air release keys, bleed keys and air vent keys.

Square headed bleed screw with slot for screwdriver Bleed keys are for loosening and tightening the square headed bleed screw located in the middle of the bleed plug at either the top left or top right of a radiator. Some also have a slot in them for a screwdriver, like this one, but a bleed key is less likely to damage the bleed screw.

See How to bleed a radiator for a step-by-step guide to this procedure.

Carded radiator bleed keys Some bleed keys are sold ‘carded’ – that is, they are laminated to a printed card and may be sold in multiples of two or more.
Bleed key for rear mounted bleed valves and normal key Bleed keys can be made from brass, zinc-plated brass, nickel-plated iron, copper, aluminium, zinc-plated steel or alloys, which are mixtures of two of more metals. These metals or coatings are used because they will not rust.
Clock style radiator air release key Some bleed keys are shaped like clock keys.
T-shaped radiator bleed key Others follow a simple ‘T’ design.
Long wire handle rear entry air release key Some bleed keys have a long wire handle for a particular reason…
Bleed screw in back of radiator …Some older radiators have their air vent plugs inserted into the back of the panel and are difficult to turn with a normal key. The rear access key makes the job much easier.
Radiator bleed key with bottle At the critical stage of bleeding a radiator, water squirts out, which can sometimes be a bit messy even if you use a cloth to try to catch it.

There are keys that include a bottle to catch the water, so there is never any mess.

Alloy radiator bleed key You might think a cheap alloy key isn’t as good as a more expensive one. However, it does have an advantage.

Because the key’s metal is softer than the bleed screw, it is less likely to damage the bleed screw head than harder keys.

Damaged radiator bleed screw One of the most common things to go wrong with radiators is damage to a bleed screw. If the screw’s square edges get worn, it might become impossible to turn it.
T-shaped alloy radiator bleed key For a step-by-step guide to using these keys, see: How to bleed a radiator

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