Banging, knocking or gurgling from your heat?

Steam hammer

On steam systems, banging usually means condensed water is trapped in a pipe or radiator and steam slams into it. Pipes that sag or radiators tilted the wrong way are common causes in older houses. See steam boiler repair.

Gurgling

Gurgling in baseboard or radiators often means air in the system, which can usually be bled out.

Banging in steam systems

Steam hammer is the loud bang or knock you hear when steam hits a slug of water trapped in a pipe or radiator. It is common in older Utica houses, where steam systems are often a century old and the house has settled. The water gets trapped where pipes have sagged, where radiators have tilted the wrong way, or where the boiler water level is set too high.

Check radiators first. On one pipe steam, each radiator should tilt slightly back toward its valve. The valve must be fully open. A radiator with a half closed valve or a backward tilt is a classic banger.

Kettling in the boiler

Kettling is a rumbling, popping or whistling inside the boiler, like a kettle about to boil. It happens when scale or sludge on the heat exchanger traps water, which boils in small pockets. It is more common in areas with hard water and in older systems that get a lot of fresh water added over the years.

Kettling reduces efficiency and can overheat parts. The fix may be a system flush, a descaling treatment, or correcting low flow. If a high efficiency boiler kettles, check that the circulator is running and that flow is not blocked.

Writing down the noise

Record a short video with sound on your phone, and note when it happens: at startup, while running, when the heat shuts off, or at night as the house cools. Note where it is loudest. That timing tells a technician a lot about the cause and saves time on the visit.

Older Utica homes

Census estimates put about half of Utica's housing as built before 1940, and that is where most steam systems are.^[source] Decades of settling, renovations that moved radiators, and boiler replacements with different water lines all create places for water to collect. A technician who works on steam regularly can often quiet a system by finding those places.

Steps you can try for steam banging

With the boiler off and cool, look at the sight glass. If the water is well above the normal line marked on the boiler or in the manual, the boiler may be overfilled, often by an automatic feeder or by someone adding water by hand. Too much water lets steam carry water into the mains, and that water bangs. A technician can drain it to the right level and check the feeder.

Next, walk the basement and look at the steam mains, the larger pipes leaving the boiler. They should slope steadily, either back toward the boiler or toward the end of the main, depending on the design. A main that sags between hangers holds water. Replacing a broken hanger or adding one can stop the bang.

Then check each noisy radiator for pitch and a fully open valve. Keep notes on which radiators bang and when. Noise near the boiler in the first minutes of a cycle points to near-boiler piping or water level. Noise at a single radiator points to that radiator or its branch.