Many homes and apartments use hot-water boilers to keep comfortable in winter. They are relatively efficient, but not always easy to fix. Fortunately, understanding how they work and maintaining them can make them trouble free longer. Also see the Steam Boiler Fix-It Guide .

How Does It Work?

Components of a typical hot water boiler.

A hot-water heating system consists of a boiler to heat (but not boil) water, a network of pipes that distributes the water, and radiators that heat various rooms. A hot-water heating system uses the same type of boiler that a steam heating system uses. Controls include a combination gauge (or altitude gauge) that lets you check water temperature and pressure and lets you know when the boiler needs water or is malfunctioning. In some systems, a pressure-reducing valve takes care of the water automatically. The typical system also has an expansion tank that must be properly charged with air to prevent the water from boiling. Newer systems usually locate the expansion tank on the basement ceiling near the boiler; they also include a purge valve to release water and let in air as needed. Older systems sometimes have the expansion tank in the attic and include a gauge glass similar to that on a steam boiler.

What Can Go Wrong?

Because they have few mechanical parts, hot-water heating systems usually perform reliably for many years. The most common problems are with the expansion tank or a circulator rather than the boiler. Here are some symptoms of problems: A hot-water system may produce no heat or poor heat and leaks can occur. Some radiators may not heat while others do. Pipes may make a clanging noise.

Fix-It Tip

Place a pan of water on top of a radiator to add humidity to the air during the winter, if needed.