How to Troubleshoot a Hot Water and Steam Distribution System

Hydronic hot water systems use a motor-driven circulating pump to move the [b]hot water. The water moves rapidly and arrives at the radiator with little heat loss.
©2006 Publications International, Ltd.

Hot water and steam systems work similarly, but neither are typically installed in newer homes. However, because both are still in existing homes, here are some maintenance tips for them.

Because water retains heat, it is used to store and distribute heat in home systems. There are two types of hot water systems: the gravity system and the hydronic or forced hot water type. Hot water heating systems can be powered by gas, oil, or electricity.


Gravity systems depend on the upward flow of hot water to circulate heated water from the boiler through a system of pipes to radiators in the rooms of your home. The better radiators for hot water systems are called convectors. These units employ a series of fans to disperse the heat.

The heat from the water in the radiators or convectors is transferred first to the metal radiators and then to the air. As the water loses its heat, it sinks and flows back to the boiler through return pipes. Most gravity systems heat the water to no more than about 180 degrees Fahrenheit, and cooled water that goes back to the boiler rarely falls below 120 degrees Fahrenheit.

Open gravity systems have an overflow outlet to let water escape; this prevents a buildup of excess pressure in the system. Closed systems have a sealed expansion tank; when water pressure builds up in the system, the excess water flows into the expansion tank to prevent damage to the pipes or the boiler. Hydronic hot water systems are much like closed gravity systems, except a hydronic system uses a motor-driven circulating pump to move the water. As a result, water in a hydronic system moves more rapidly and arrives at the room radiator with less heat loss than water in a gravity system.

There are other key factors to consider when maintaining a hot water and steam distribution system. Learn these maintenance guidelines in the next section.


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.


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.


Flushing and Draining Techniques

Once a year, the entire hot water and steam system should be flushed to keep the pipes clear and the water flowing freely. To flush the system, open the blow-off valve and let the water run off into a bucket until it runs clear. If the water still looks rusty after the system has been flushed, call a professional service person.

Hot water systems should be drained to prevent the pipes from freezing during a prolonged cold weather power failure. It may also be necessary to drain the system to make repairs. Here's how to drain the pipes:


  1. Turn off power to boiler, and let water cool until it's just warm.
  2. Turn off water supply valve, and attach length of garden hose to boiler drain.
  3. Open drain valve and air vents of all radiators. Water from system will flow out through hose. Give valve plenty of time to drain.
  4. To refill system, close air vents on all radiators, and shut drain valve. Turn on water supply to boiler. If boiler has automatic shutoff, refilling is automatic. If there is no automatic shutoff, fill it until combination valve gauge reads 20 pounds of pressure per square inch (psi).
  5. Release air from all convectors in system so they'll heat properly. Gauge on boiler should read 12 psi.

If pressure on gauge shows less than 12 psi, add more water. If pressure is above 12 psi, drain off some water.

If you follow the steps in this article, you can be assured that your hot water and steam system will operate efficiently for years to come.

Note: There are myriad problems that can cause your system to malfunction. Click here for a troubleshooting guide for hot water systems, and click here for one on steam systems.

© Publications International, Ltd.


Hot Water Steam System FAQ

What are steam boilers used for?
Hot water boilers may heat up homes or businesses. They also may have industrial applications such as powering turbines or providing steam in hospitals for sterilization purposes, for example.
What water temperature do most hot water boilers heat up to?
The standard setting is 140 degrees F (60 degrees C), however, you can set it lower (120 degrees F or 49 degrees C) if you're worried about your heating bill and/or would like to be more energy-efficient.
Are a boiler and hot water heater the same thing?
A hot water heater heats water, while a boiler can both heat your home and heat water.