Repairing Old Radiators


Many older homes are heated with steam or hot water radiators. Newer homes may have convectors. You can make minor repairs to radiators, but leave problems with a boiler or piping to a professional.

A steam radiator has a small air vent near the top that emits bursts of steam when the radiator heats. Steam systems cycle between hot and cold. Most are connected to only one pipe at the floor, but some have two. You can dismantle and service a steam radiator valve if the boiler is off. It can be difficult to work on, however, because the high heat tends to seize up the pipe joints.

Hot water radiators are connected to two pipes at the floor. They maintain a constant warmth, rather than cycling between hot and cold. Before you dismantle a hot water radiator valve, you must drain the system.

Prestart Checklist

About two hours, plus time for finding the parts

Groove-joint pliers, pipe wrench, screwdriver

Familiarity with your system

Turn down the thermostat so the boiler will not come on while you work

Radiator valve replacement parts or a new valve, strand packing, pipe-thread tape

Installing a new valve: Step 1

If water leaks from beneath the handle, turn down the thermostat and wait for the radiator to cool. Tighten the packing nut (just under the handle) using groove-joint pliers and tighten the larger union nut using a pipe wrench. If this does not solve the problem, move on to the next step.

Installing a new valve: Step 2

With a hot water system, water must be drained from the radiator. Turn down the thermostat. Attach a hose to the boiler's drain valve and run the hose to a floor drain; open the valve to drain the system. Starting at the top floor of your house, open the bleeder valves of all radiators.

Installing a new valve: Step 3

Unscrew the packing nut and remove the stem, first by unscrewing and then by pulling it out. If the leak originates just under the handle, wrap the stem with strand packing and reinstall. If the leak is lower or if this does not solve the problem, replace the valve (Step 4).

Installing a new valve: Step 4

Unscrew the union nut that attaches the valve to the radiator, then unscrew the valve from the pipe. Take the old valve to a plumbing and heating supply store to find an exact replacement; look carefully to be sure it will fit. You also may need to replace the short pipe that emerges from the radiator.

Repairs to Radiators: Vents

A steam radiator valve must be turned either all the way on or all the way off. To adjust the heat, an adjustable air vent is used. Turn down the thermostat and use pliers to unscrew the old air vent. Buy a compatible adjustable unit. Wrap the threads with pipe-thread tape and screw the new unit in place.

Repairs to Radiators: Bleeder Valves

If a hot water radiator is not heating enough, air may be trapped inside. Turn the thermostat up and wait for the radiator to get warm. Hold a cup under the bleeder valve and open it with a bleeder key, long-nose pliers, or screwdriver. Spluttering water or hissing air may come out. Once water flows in a steady stream, tighten the valve.

Repairs to Radiators: Air Flow

To improve a radiator's performance, move furniture and other obstructions out of the way. Air should flow freely under and above the radiator. A sheet of aluminum or reflective insulation placed behind the radiator directs more heat into the room.

Comments (5)
tullula1tullul wrote:

Great info! All remember to monitor room humidity with all radiant heat. So important! See unique humidifiers and aromatic diffusers especially for antique style radiators at

10/20/2016 02:02:01 AM Report Abuse
scottmltnaolc wrote:

I need a plumber in my are that can repair my old radiators in Washington, DC 20002.

8/26/2016 03:35:01 PM Report Abuse
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