Bleeding fixes trapped air. If the cold spots come back within weeks, air was never the real problem.
Turn the heating off and let the system cool. Bleeding a hot radiator risks scalding and gives a misleading result.
Start with the radiator furthest from the boiler, on the highest floor. Hold a cloth under the valve, turn the key a quarter turn anticlockwise, and close it the moment water appears instead of air.
Re-check the boiler pressure afterwards. Most systems want between 1.0 and 1.5 bar cold; bleeding drops it, and running a system below 1 bar shortens pump life.
If a radiator is cold at the bottom rather than the top, that is sludge, not air. Bleeding will do nothing. That radiator needs flushing, and usually so does the rest of the system.
Cold spots that return within a few weeks nearly always mean the system is drawing in air somewhere — a failing auto air vent, a pinhole leak, or an incorrectly sized pump. That is worth investigating rather than repeating.
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