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Why Do My Radiators Make a Banging Noise?

June 08, 2022

In homes with radiators, heating starts at the boiler. Water is heated in the boiler before traveling through pipes to the radiator. Once there, the water transfers its heat to the air around the radiator by convection. The air around the radiator gets warm and rises, and new, cool air surrounds the radiator to take its place. This process repeats until the water is no longer hot. Then, cooled water travels back to the boiler to be reheated.

Noisy radiators aren’t just annoying; they’re probably wasting your money since they point to inefficiencies in your heating system. If you hear banging coming from your radiator, it usually is caused by one of the following conditions:

  • Air bound radiator
  • Problems with radiator valve
  • Improperly sloped radiator
  • Dirty boiler water

Let’s walk through each of these conditions in more detail to help you pinpoint what may be the cause of your noisy radiator(s).

If you’re bothered by persistent banging, hissing, or knocking noises coming from your radiator, it’s time to have it evaluated by a professional. At Ranshaw Plumbing and Heating, our highly trained heating technicians can perform same-day repairs on your heating system when you need it. To schedule service, call us at (718) 767-0707 or book online today.

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Air Bound Radiator

Bleeding your radiators will release any air that may be trapped inside.

When air gets into your heating system, it can cause a banging noise because it increases the pressure in the system. Releasing pressure by bleeding the pipes of excess air can stop the banging noise from occurring.

To bleed your radiator’s pipes (NOTE: this is for hot water systems only as steam radiators have air valves that automatically release excess air), start by turning off the heat entirely and letting your radiator cool for 30–60 minutes. It should be cool to the touch before you move forward. After cooling, turn the pressure release valve to let extra air out and release unnecessary pressure. This should stop the banging noises from occurring when you turn your heat back on. Keep in mind that radiators in certain types of hot water systems do not have a bleeder valve. If that’s the case, a heating contractor will be able to help bleed your system.

Problems with Radiator Valve

Heating systems work in a closed loop circulating hot water/steam from radiator to radiator throughout your home.

Partially Closed/Leaking Radiator Valve

The radiators in your home are connected by pipes that are controlled by valves. Partially closed radiator valves in a steam system may be trapping condensation in your radiators instead of allowing it to flow back to the boiler (i.e., return), which can cause a banging noise when new hot water enters the radiator.

Broken/Leaking Valve

Radiator valves control water flow from one radiator to the next in your home. Valves help prevent water from releasing all its heat at the first radiator by limiting the amount of water that flows into the radiator. However, when valves are loose/leaking, they can allow too much water to enter the radiator, which can cause standing water to accumulate in the radiator.

Since your heating system works in a closed loop, water travels from the boiler to the line of radiators and back. End-of-the-line radiators are being warmed by water that's already released a lot of its heat.

The banging noise occurs when new hot water is released into a radiator that contains standing cold water. New water enters the radiator at high speed, slamming into the standing water and against the metal walls with a loud bang.

Improperly Sloped Radiator

A wrongly pitched steam radiator can produce loud banging noises.

Contrary to popular belief, steam radiators do not need to be “level” to the floor, so leveling a steam radiator to the floor will not stop banging noises.

These steam devices must be “pitched” downward to return condensate to the boiler as only one pipe connects to the radiator. Any steam entering the pipe heats up, condenses, and then forms water that goes back to the boiler. With only one pipe, a sloped radiator prevents water from becoming trapped and incoming steam from trying to force its way past the trapped water, which can cause banging noises.

To pitch a steam radiator the right way, it should slant slightly towards the valve for water to drain out easily. Place an instrument called a "spirit level" on top of the radiator to check that it is slanting towards the valve. If it’s not, put wooden shims (slim blocks) under the radiator’s legs on the opposite end of the steam pipe.

Dirty Boiler Water

Flushing a boiler removes contamination and debris from your boiler’s water supply.

If the water in your boiler becomes contaminated by dirt or sediment, it can restrict steam from being evenly distributed throughout your heating system. When the boiler produces “wet steam,” this can create a banging noise at your radiators.

To address this, your boiler will have to be drained of its water entirely before flushing it with a chemical treatment, which is known as a chemical flush. A chemical flush removes the sediment buildup, allowing your boiler to produce a clean, efficient supply of steam. Being that a chemical flush is a very controlled, multi-step process, it should be left to an experienced heating professional.

Keep Your Heating System Running Quietly and Efficiently with Regular Tune-Ups from Ranshaw Plumbing & Heating

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Call Ranshaw for a reliable and efficient heating tune-up.

The best way to keep your heating system running efficiently is to have a heating tune-up performed annually. If remembering to schedule service is too difficult, consider joining our maintenance plan for annual tune-ups, priority scheduling, and discounts on installation and repair work.

We’re experienced, trustworthy heating professionals with 60+ years of service under our belt. When you need heating service, contact Ranshaw Plumbing & Heating for a job done right the first time. Give us a call at (718) 767-0707 to schedule an appointment.

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