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Maintaining Home Radiators


Before the heating season begins, it's important to perform routine maintenance of your radiators to assure proper and efficient operation. For a hot-water system, air can be trapped in the upper sections of the radiator and block the circulation of hot water to these areas. If there is no water, there will be no heat. In a steam radiator system, faulty steam traps or air vents or an improperly pitched radiator can cause similar inefficiencies. Here are the basics for routine maintenance of your home radiators.


1. Clean/Replace Air Vent: In one-pipe steam heating systems, an automatic air vent on each radiator allows air to escape but closes when in contact with steam. If both your thermostat and heating unit are working properly, and a radiator does not heat up, the air vent may be clogged. To remove the clog, close the shutoff valve at the bottom of the radiator and unscrew the air vent. Boil it in a solution of vinegar and water for about 25 minutes. If that does not correct the problem, replace it.


Tip: More often than not, shutoff valves are frozen shut. If that is the case, you must shut off the heat first and allow the system to cool before removing the air vent.


2. Shim a Steam Radiator: Steam radiators should pitch about 1 inch every 10 feet either toward the trap (in a two-pipe system) or toward the inlet pipe (in a one-pipe system). Over time, the feet can dig into the floor causing an improper pitch. This can cause a banging noise as steam becomes trapped by water or air in pipes and the pressure builds. Check for proper pitch with a level and place shims under the legs, as necessary.


Tip: While hot-water radiator valves can be opened or closed partially to control heat, steam valves must be fully open or closed. You can replace a standard air vent with an adjustable air vent, which allows for similar control. Do this in the off season by closing the shutoff valve, unscrewing the old vent, and screwing in the new one.


3. Test Steam Trap: A steam trap, which is located at the bottom of each radiator at the outlet pipe in a two-pipe system, routs condensation back to the boiler. Mineral deposits can cause it to either stick open, causing system balance problems, or remain closed, which keeps the radiator from getting hot. Tracking down which trap is bad is a complicated, hit-or-miss process. A lack of heat may indicate a trap is stuck closed but it can also indicate that another trap is stuck open. If the pipe below the trap is not 10-15 degrees colder than the inlet side, the trap is stuck open. Measure the temperature of the pipes with a tempil stick or electronic thermostat. (Traps rarely last more than 5-10 years, so if you have problems with an old system, your best bet may be to replace them all.)


4. Replace Steam Trap: Turn off the system. Unscrew the trap and remove the element inside, which may be attached to the cap or the base of the trap. Buy replacement modules at a plumbing and heating supply outlet, and secure them as directed before reinstalling the caps.


Tip: Finding information about steam heating systems and professionals experienced in steam heat is very difficult. We recommend a book called The Lost Art of Steam Heating by Dan Holohan.


5. Bleed Radiator: In a hot-water system, air trapped in a radiator is bled manually. The bleed valve is located at the top end of the radiator and at one end of the baseboard convector. Start on the top floor and work down. Hold a container under the valve and turn the valve stem about a half turn or until air and water flows out. Slotted stems are turned with a screwdriver and square ones are turned with a radiator key. Shut the valve as soon as only water is being drained.


Tip: Running the circulator often facilitates the bleeding process, but that means the boiler is on and the water can be very hot. Be very careful if you plan to run the circulator. !


Tip: A properly operating hydronic system seldom needs to be bled. If you find air in the system again at mid-season or season after season, don't just keep bleeding the system. Have your system checked by a professional. There is probably a leak in the system, possibly at the expansion tank, or improper piping at the boiler.