A cold radiator does not always mean something is broken. In many hot water heating systems, air can become trapped in the piping and prevent hot water from circulating. When that happens, the boiler may be running normally while the radiator stays cool. Opening a small bleed valve at the radiator can release air in simple cases, but it does not always solve the problem. If air is trapped deeper in the heating loop, the only effective fix is purging the line from a boiler drain so water can forc