How to Repair Radiators and Keep an Old Heating System in Tip-Top Shape

Anyone who's lived with radiators knows their downsides, like occasional clacking and hot-to-the-touch metal. But live with one long enough, and you'll become well-versed in the pros, too: This heating method is efficient and doesn't dry out the air, creating a coziness that forced air can lack. If you're sold on your old-fashioned system and want to keep it up and running for years to come, it pays to learn a few home radiator repairs.

The first step is identifying what type of radiator you have. Many older homes are heated with steam or hot water radiators, while newer homes may have convector radiators. Below, we help you figure out which variety heats your home, then walk you through basic radiator repairs: installing a new valve, clearing the bleeder valve, and maximizing airflow, for example.

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. Keep 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 on your own, but you should leave problems with a boiler or piping to a professional.

How to Identify Steam and Hot Water Radiators

Steam Radiators

This type of radiator quickly heats up when the boiler fires, emitting bursts of steam from a small air vent near the top. The steam travels through the pipes to warm your home, then cools off, condenses into water, and returns to your boiler; as a result, the system cycles between hot and cold. Typically, a steam radiator is connected to the floor with only one pipe, although some have two. If your radiator ever whistles, it's probably powered by steam.

You can dismantle and service a steam radiator valve if the boiler is switched off. This type can be difficult to work on, however, because the high heat tends to seize up the pipe joints.

Hot Water Radiators

In a hot water system, heated water continually circulates through the radiators, which are always connected to two pipes on the floor. These systems maintain constant warmth, rather than cycling between hot and cold.

Before you dismantle a hot water radiator valve, you must drain the system.

How to Fix a Leak Beneath the Handle

Step 1: Tighten Nuts

If water is leaking from beneath the handle, turn down the thermostat and wait for the radiator to cool. Tighten the packing nut (located just under the handle) using groove-joint pliers and tighten the larger union nut using a pipe wrench. If this doesn't 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, then attach a hose to the boiler's drain valve. Run the hose to a floor drain, and 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 the next step.

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; check carefully to ensure it will fit. You also may need to replace the short pipe that emerges from the radiator. Screw on the new valve and put the union nut back on, replacing the pipe first if necessary.

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 needed. 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 warm up. 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 will direct more heat into the room.