Bleeding radiators is typically done on a regular maintenance schedule and when you notice signs of air in the system. The common guidance is to bleed once a year, usually before the heating season begins, and more often if you observe cold spots, noisy operation, or slow heating. What to check and when to bleed

• Signs that you may need to bleed: cold spots at the top of a radiator, radiators taking longer to heat up, gurgling or banging sounds, or after a long period of not using the heating (summer downtime) [web results reflect standard industry guidance].
• Ideal timing: once a year in autumn is a widely recommended timeframe to ensure the system is ready for winter [web results].
• Do not bleed while the heating is on: bleeding hot radiators can be dangerous and may reintroduce air into the system; perform bleeding with the system cool or only slightly warm and with the boiler off when needed [common maintenance guidance].
• If bleeding doesn’t fix the issue: persistent cold areas or lack of heat after bleeding could indicate valve blockages or sludge buildup, which may require a professional service [typical troubleshooting guidance].

How to bleed a radiator (quick steps)

• Have a cloth and a small container ready, and identify the bleed valve (usually at the top corner of the radiator with a square or slotted valve).
• Use a radiator key or screwdriver to slowly open the valve a quarter to half-turn until you hear a hissing, then close it when water begins to escape.
• Once air stops and water begins to come out, tighten the valve firmly and wipe up any water.
• Check that the radiator heats evenly—top-to-bottom—and repeat on other radiators if needed.

If you want, I can tailor these recommendations to your system specifics (type of radiator, boiler, and climate) and suggest a simple annual maintenance checklist.