How to Repair Old Radiators

Radiators can be finicky—but that doesn't mean you have to live in the cold. We'll walk you through basic repairs for old radiators.

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Knowing how to repair your radiator will help you stay warm during the winter months. But before you begin, it's important to know what type of radiator you have. Many older homes are heated with steam or hot water radiators, while newer homes may have convectors.

We'll walk you through basic radiator repairs: like installing a new valve, clearing the bleeder valve, and maximizing air flow. Expect to spend anywhere from a few minutes to a few hours on these projects, and make sure you're familiar with your system before you begin. Have basic tools on hand—like groove-joint pliers, a pipe wrench, and a screwdriver—plus any new parts you may need. 

Editor's Tip: You can make minor repairs to radiators, but leave problems with a boiler or piping to a professional.

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Identifying Hot Water and Steam Radiators

In a steam system, steam quickly heats the radiator when the boiler fires. In a hot water system, heated water continually circulates through the radiators. 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.

How to Install a New Valve

Step 1: Tighten Nuts

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.

Step 2: Drain the Radiator

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.

Step 3: Wrap the Stem

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, continue to step 4. 

Step 4: Replace Valve

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.

How to Install a New Handle

If a handle is cracked or loose, remove the top screw and pull off the old handle. If the stem's threads are in good shape, buy a replacement handle that has the same size screw. If the stem is damaged, buy a "fits-all" handle, which clamps onto the stem with a setscrew.

How to Install an Adjustable Air Vent

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.

How to Adjust the Bleeder Valve

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.

How to Maximize 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.

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