Like HowStuffWorks on Facebook!

How to Troubleshoot a Hot Water and Steam Distribution System

Slope, Water Level, and Expansion Tank

The following are key factors to consider when servicing a hot water and steam system.


Hot water systems depend on proper slope. All pipes and radiators must slope back toward the boiler. Hammering noises and failure to heat indicate incorrect slope. To correct these malfunctions, check the slope of radiators and pipes, and prop radiators or fasten pipes so all components are properly tilted.

Water Level

The water level in a hot water system's boiler should be maintained at about half full. There should be an air space between the surface of the water and the top of the tank. A water level that is too low can cause inadequate heating.

In most cases, an automatic filling system keeps the boiler filled with the proper amount of water. However, if the water level of the system is consistently low, check the pipes for leaks. Close the water supply valve and note the water level for two or three days. If the level drops drastically, call a professional service person.

Expansion Tank

For efficient heating, the water in a hot water system is heated well above boiling, but it doesn't turn to steam because the expansion tank and a pressure-reducing valve keep the water under pressure. Usually the expansion tank is hung from the basement ceiling, not far from the boiler.

In older systems, look for the expansion tank in the attic. If there is not enough air in the expansion tank, the buildup of pressure will force water out of the safety relief valve located above the boiler. Without enough air in the tank, the tank fills with water. The water expands as it heats up and then escapes through the safety relief valve.

Check for air in the expansion tank by lightly touching it. Normally, the bottom half of the tank feels warmer than the top; if the tank feels hot all over, it has filled with water and must be drained. Here's how to drain an expansion tank:

  1. Turn off power to boiler. Close water supply shutoff valve, and let tank cool.
  2. A combination drain valve lets water out and air in when it's opened. If there is a combination valve, attach garden hose to valve and drain 2 or 3 gallons of water. If there is no combination valve, shut off valve between expansion tank and boiler, and completely drain expansion tank.
  3. Turn water supply back on. Then turn on power to boiler to get system running again. It isn't necessary to refill expansion tank; it will fill up as part of system's normal operation.

Radiators on a hot water and steam system require regular servicing and maintenance. The next section will tell you all you need to know about it.