Troubleshooting Steam Radiator Problems

Old style cast iron household steam radiator for heat
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Radiators for steam boiler heating systems can be prone to behavioral problems. Fortunately, many of these problems are quite easy to fix, with no need to call a heating system technician. On single-pipe steam systems, many of the problems can be traced to the air vent fitting.

How Steam Radiators Work

If your heating system uses a boiler, it can be of two different types: hot water, or steam. It is not always easy to know which type of system you have. In hot water boiler systems, the radiators will always have two pipes attached at opposite ends of the radiator. One pipe delivers hot water to the radiator from the boiler, and the other pipe carries cooled water back to the boiler for reheating. You can generally identify a hot water system by the presence of an expansion tank, usually located near the boiler itself. And there will also be an electric water pump connected to the boiler, generally mounted on the cold water return pipe leading to the boiler.

In a steam system, on the other hand, the pipes carry gaseous steam vapor rather than hot water to the radiators. A steam radiator can look quite similar to a hot water radiator, but with a steam system, the boiler doesn't require an expansion tank, nor does the system require a water pump.

Steam systems can be one-pipe or two-pipe systems. In two-pipe systems, each room radiator will have two pipes attached to it, one at each end. One pipe delivers gaseous steam to the radiator, while the other carries condensed water back to the boiler. Or, you may have a one-pipe system, in which the same pipe delivers steam to the radiator and also carries condensed water back to the boiler. If you see only one pipe attached to your radiators, you can be assured you have a one-pipe steam system. In one-pipe systems, you should find an air vent fitting on one end of the radiator. This air vent is often the source of problems in a steam radiator.

The air vent on a steam radiator allows air in the cooled radiator to be pushed out to make room for the incoming steam as the heating cycle begins. The hissing sound of the air venting from the valve is a sign of normal operation, but the noise should stop once the radiator comes up to temperature and the vent closes, thereby retaining steam in the radiator so it can give up its heat and condense back into water.

Here are some common problems to watch out for with a steam radiator.

Radiator Makes Gurgling Noises

If a steam radiator makes gurgling noises, either from the air vent or from the radiator itself, it's usually a sign that condensed water is being trapped in the radiator rather than draining back down to the boiler. This can be the result of problems with the radiator itself, the control valve, or the air vent. If you hear gurgling sounds from your steam radiator, check for the following conditions:

  • Make sure the supply valve is fully open (turned counterclockwise all the way) and that it operates properly. If the valve is corroded or stuck, repair or replace the valve. If this valve isn't fully open in a one-pipe system, it may be preventing condensed water from draining out of the radiator, leading to the gurgling noise.
  • Check the radiator's slope. In a one-pipe system, the radiator should slope slightly toward the end of with the supply valve. Shim under the feet of the radiator as needed to achieve a proper pitch of 1 inch for every 10 feet toward the supply valve. With two-pipe systems, make sure the radiator is sloped in the opposite direction, toward the return pipe.
  • In one-pipe systems, make sure the air vent is positioned vertically. Make sure it is not pointing upside down, diagonally, or sideways. Usually, you can simply rotate the valve clockwise to the vertical position (it's threaded into the radiator).
  • Inspect the air vent to check for obstructions caused by mineral deposits or other debris. Try to clean the vent with vinegar. If you can't blow air through the vent after cleaning, replace the vent.

Air Vent Constantly Hisses

A constant hissing sound throughout the heating cycle usually means the air vent is not closing at the right time and is failing to trap the steam inside the radiator. Try to clean the valve with vinegar. If that doesn't solve the problem, replace the valve.

Radiator Doesn't Heat Up

If the radiator doesn't heat up, it often indicates that the air valve is stuck shut, blocking cold air inside the radiator and preventing steam from entering. Try to clean the valve with vinegar, or simply replace the valve. Also, check for these conditions: 

  • Make sure the supply valve is fully open (turned counterclockwise all the way).
  • Check to see if the thermostat in the room (as applicable) is set too low. Confirm that the thermostat is set above the current room temperature.
  • Check to see if the radiator is sloped properly. On one-pipe systems, it should slope slightly toward the end of the radiator with the supply valve and pipe. Shim under the feet of the radiator as needed to achieve a proper pitch of 1 inch for every 10 feet toward the supply valve. On two-pipe systems, the radiators should slope away from the supply valve and toward the return pipe.

Air Vent Spits or Leaks Water

An air vent that's spitting or leaking water may be partially obstructed with mineral deposits or other debris. Try to clean the valve with vinegar. If that doesn't solve the problem, replace the vent.