When radiators in a hot-water system develop banging or hammering noises the problem is most often due to trapped air that cannot get out. Air gets into the system from the fresh water that is periodically added to the system (usually automatically) to replace water that evaporates or leaks out.

How do I stop my radiators from banging?

Other explanations can include a dirty boiler or a back-pitched pipe. If your valves are correctly positioned and intact, you may be able to stop the banging by shimmying up one side of the radiator so that it tips toward the boiler and prevents water from settling.

Why do radiators clank when heating up?

Your Heating System Uses Forced Water

When water is heated, it expands. However, expansion in a limited space like a pipe or radiator sometimes leads to a condition known as "air-bound" pipes. This can cause air bubbles to become trapped, which leads to a clanking or hammering noise in your pipes.