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How to bleed a radiator

Bleeding radiators isn't real plumbing. It's like letting the wind out of a mechanical cow. Just as a cow's four stomachs lead to its prodigious gas output, your central heating can get air trapped, too. Water expands when heated, so every time your boiler comes on, the radiators' water takes up more room than it did a minute ago (that's why you have an expansion tank in the loft for it to expand into). When it contracts again, it can suck in air. Air also gets in through small leaks (surprisingly common, particularly around radiator valves ) during expansion and contraction. A classic symptom of trapped air is if your radiators don't get warm at the top. You may also hear ruminant-style gurglings. Get a radiator key. Locate the bleed nipple, or valve shank, usually on a top corner of the radiator, and try your key . Now go back and buy one the right size (they're not standardised). Standing by with an old mug for catching water and an old towel just in case, slot in your key. Turn it a quarter of a turn anticlockwise; no more or you'll get covered in brown stuff. Leave the air leak to flow out (this may take some time) until a spit of water begins, then shut it off. Top tip: Dale Courtman, Britain's Top Plumber, says the experts then give it another quick quarter turn. That's £50 you've saved. If you need to bleed your radiators more than once every year or two you could have Expansion Tank Valve Grief, which should be addressed sooner rather than later, because air in the system means rust. Rust is cholesterol for central heating, and you don't want the old girl to get that, as it can lead to major central heating surgery.

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