Noisy radiator: 8 possible noisy radiator causes

Got a noisy radiator or noisy central heating pipes? If they’re making banging, hammering, vibrating or hissing noises, it may certainly come as shock when you turn the boiler back on for the winter. In this article, we’ll discuss the most common reasons for all those different noises, and how they can be fixed.

The noisy radiator explained

Firstly, it’s worth mentioning that, depending on your system, some radiator noises may be completely normal. For example, a slight hissing sound of water from inside may simply be the result of your thermostatic valve restricting the flow of water so that the radiator doesn’t exceed the desired heat setting.

Of course, there are some sounds which radiators and pipes definitely shouldn’t make, such as banging, clunking, gurgling and vibrating sounds. In some cases, the resonance may be substantial enough to create a hammering sound, much like water hammer.

To start with, there should only ever be two things inside them: water, and central heating inhibitor. The inhibitor is a chemical which stops corrosion by preventing the water from reacting with the metal of your radiators. Anything else is likely to have an adverse effect – and that often manifests as banging, clanking or gurgling noises.

Air

One of the most obvious unwanted things in your radiators is air. This is a result of oxygen bubbles and other gases forming inside your central heating system. The air takes up space in the radiator which should be occupied by hot water. As a result, the radiator may not get hot at the top, or it may take a long time to heat up.

Bleeding the air out may very well fix a noisy radiator and is something you can do yourself. Click here to learn how to do it.

You should bleed the radiators at least once a year, generally before the start of the season. If you find that you keep having to bleed the radiators more frequently, then this may indicate another problem, such as the lack of a chemical inhibitor. Alternatively, if you have an open vented system – i.e., you have a feed and expansion tank in the loft – then air may be getting sucked into the system via the expansion pipe.

Sludge

Sludge is a result of corrosion inside your central heating system. It consists of metal oxides which range in a colour from a dark brown to a deep black. 

Sludge can block your radiators and pipes, and it can definitely be a cause for a noisy radiator. Other signs of sludge include:

  • Radiators which don’t get hot at the bottom
  • Excessive noise from the boiler
  • Dirty, discoloured water when you bleed the radiators

Sludge can be removed by powerflushing. If you think that your system would benefit from powerflushing, contact a Gas Safe heating engineer. This is definitely worth doing if your system hasn’t been powerflushed for over 10 years. After powerflushing, adding inhibitor to the system will protect it from corrosion in future. Consequently, it will also help prevent the formation of unwanted gases in the system, as one of the byproducts of the corrosion process is hydrogen.

Pump speed is too high

An improperly configured central heating pump can certainly be the cause of noisy radiators or pipes if the pump is set too high. Setting the pump to a lower speed may solve the problem, although it will take longer for the radiators to heat up.

For most residents, i.e., those with a combi boiler or a system boiler, it probably will not be possible to change the pump speed. That’s because the pump is fitted inside the boiler, and usually isn’t a separate component in an airing cupboard.

The natural expansion of metal

It’s usually completely normal for your radiators and pipes to make ticking, clicking, or popping sounds. In most cases, it’s simply the sound of the metal expanding and contracting as it heats up or cools down.

You may also hear these sounds coming from within the walls of your house, if your pipes are chased into them. Plastering directly over pipes can prevent them from expanding naturally and will encourage such sounds.

Your radiators need balancing

Too much water flowing through a radiator may very well create unwanted rushing or hissing noises. Your system may need balancing, especially if your radiators furthest from the boiler don’t get as hot as the others. That’s because the water will naturally take the shortest route back to the boiler. Consequently, you may also have rooms which get too warm, and others which don’t get warm enough.

By controlling how much water flows through each radiator via a small valve known as a lockshield, you can ensure that hot water is evenly distributed throughout the system. As a result, this may stop any rushing rushing or hissing noises from a noisy radiator.

Hissing noise of air

If your radiator is making a hissing noise and it sounds just like air, then it probably is air. Some radiators are fitted with automatic bleeding valves or air release valves (ARV). With these valves, you don’t need to bleed the radiators manually with a bleed key – the valve lets the air out automatically.

Poorly secured pipes

The flow of water through pipes which have not been adequately clipped to the wall may create resonance. This can manifest as vibrating and hammering sounds, resulting in a noisy radiator and noisy pipes. Vertical runs of 15 mm copper pipe should be clipped every 2 metres, and 2.5 metres for 22 mm pipe. For horizontal runs, 15 mm pipe should be clipped every 1.5 m and 22 mm should be clipped every 2 m.

Limescale

We already know that air can result in a noisy radiator, but did you know that limescale can help to produce that air? Just like in your kettle, limescale deposits can form inside your boiler. These can restrict the flow of water so much that the water gets too hot, and boils. This process is known as kettling, and it can make your boiler very noisy. (It can also be caused by sludge.) And as a result of this boiling, air bubbles form in the system.

You can prevent the formation of limescale by adding a suitable anti-limescale agent to your central heating system. This is done in much the same way as adding inhibitor fluid.

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