How to Troubleshoot a Hot Water and Steam Distribution System

Radiators, Circulators, and Leaks

Radiators and circulators are important components of a hot water and steam distribution system, so the following tips will come in handy when servicing them.


If an individual radiator is cold and both it and the pipes leading to it are tilted properly, check the radiator's inlet valve. This valve must be opened all the way for the radiator to function properly. If some radiators get warmer than others, the vents are probably not adjusted properly. Adjust the vents so the ones farthest from the boiler are opened more than the vents closest to the boiler.

Air trapped in a radiator can prevent water from entering and keep it from heating. To remove air trapped in the system, open air vent valve on unit so hissing stops and water comes out. Use screwdriver or key furnished by manufacturer to open vent. If you don't have key, look for one at a heating supply store. Close vent, then reopen it for desired heat.

Some radiators have automatic valves; they don't have to be opened or closed.


The circulator is a pump that forces the hot water to radiators throughout a house. Problems with the circulator usually occur when the coupler that separates the motor from the pump breaks. This will generally make a lot of noise. Another source of trouble with the circulator is the pump seal. If water leaks from the pump, chances are the seal is damaged. If the circulator develops either of these problems, call a professional service person.


Hot water systems are prone to plumbing leaks in the pipes and at inlet valves. Pipe leaks are frequently caused by loose connections and can be stopped by tightening the connections with a wrench. Leaks around inlet valves, however, are due to deterioration of the stem packing or the washer in the valve.

Radiator inlet valves consist of a packing nut, a valve body or stem, and a washer assembly. Here's how to replace the valve packing or the washer:

  1. Shut off boiler and let it cool. It isn't necessary to shut off water; as system cools, water will flow back out of radiator to boiler.
  2. Remove screw that holds handle in place. Unscrew packing nut, remove handle, and back out valve stem or body.
  3. Remove screw and washer at bottom of stem. Replace washer with new one of the same size and type.
  4. Install new packing while reassembling valve.
  5. Tighten all connections, and then turn system back on.

It's also important to know how to flush and drain a hot water and steam system. Learn guidelines on how to complete these tasks in the next section.