Radiator makes noise after purging


If your radiator is noisy after bleeding it, here is a tutorial to help you solve the problem. A radiator can be noisy for different reasons, before or after purging. Usually the causes will be related to air or dirt inside the system. Let’s take a detailed look in this article at the reasons why a radiator makes noise after purging it, and how to solve it in a simple and straightforward way.

The 5 reasons why a radiator makes noise after purging

A lot has been written about why a radiator makes noises, and thanks to that there is quite a bit of information available on the internet. However, this information mainly refers to the general reasons why a radiator makes noise. There is hardly any discussion about the reasons why a radiator continues to emit noises immediately after having purged it.

So let’s focus here mainly on post-purge noise. Obviously we will also talk about general reasons for noise in radiators, but we will focus on the reasons and solutions for when the radiator makes noise after purging.

Let’s go from the simple to the complex, starting with a table that summarises the 5 reasons why a radiator is noisy after bleeding it, and the direct solutions for those problems. After the following table we will go into more details.

The radiator is noisy after purging it: 5 reasons and solutions
1. Air re-entered when filling it.Purge again following a good method (see our tutorial).
2. Noise comes from suspended particles.Remove the radiator and clean it thoroughly.
3. Aluminium radiators are more prone to noise.Replace the radiators with ones made of another material.
4. The decomposition of organic residues within the system generates gases.Clean it thoroughly or wait for the residue to finish decomposing.
5. Excess water flow.Reduce the flow of water.

1. Air re-entered when filling it.

If a radiator makes noise just after purging it, this may be because the air has managed to enter the system again. This is the simplest and easiest cause to resolve. As we well know, immediately after purging the radiators, the system must be filled with water, and it is possible that air reentered it at this time.


In these cases, the solution is to purge it again, and this time carries it out methodically and with more care, not only the radiators but also the boiler. You have to make sure that the air does not go back into the system, and for that, you have to purge in a specific and methodical way.

First, you have to purge the boiler, then purge each radiator one by one, starting with the one closest to the boiler, or those on the upper floors if the house has more than one floor. We have written tutorials on this subject, to which we refer the reader: How to bleed radiators? We advise you and How to purge a boiler in 4 easy steps.

2. Noise comes from suspended particles

Any piece, tank, container, etc., that continuously contains water, especially hot water, will generate salts and minerals (especially magnesia and calcium) that will either remain in suspension or become embedded in the walls.

When these mineral residues become embedded in the walls, the heating capacity of the radiator is partially or totally reduced, and the fuel bill increases, because the boiler needs to burn more fuel to produce the same amount of heat.

On the other hand, if the mineral residues (which may be combined with rust particles) remain suspended when the water heats up and moves, the particles will tend to move and collide with the internal walls of the radiator, generating noise. This is not something that can be resolved by normal purging. This is one of the main reasons why the radiator makes noise after purging.

The solution is to disassemble the noisy radiator and clean it thoroughly, flushing it with pressurised water (with a pump or a hose connected to a tap with sufficient pressure) through its inlet, and allowing it to be expelled through its outlet.


If necessary, because a mineral crust has formed inside the radiator, it is advisable to pour in some white vinegar let it act for a few hours, and then flush with pressurised water. (For some more details on this subject, we invite you to read our article: How to repair a radiator at home.)

3. Aluminium radiators are more prone to noise

This is the reason which is most difficult to repair, in the sense that you may have no other solution than to replace the radiator with one made of another material (sheet steel or cast iron). It is true that aluminum radiators have advantages in terms of heating speed and efficiency, but they also have the disadvantage of lasting less time and causing reactions between aluminum and hot water, which generates hydrogen and noise.

This process places the cause of noise within the radiator itself and is not due to external reasons. That is, it is not that there is air in the system from the outside, but that it is generated inside, so even if you bleed it, there may often be air again. Perhaps the only way to stop those noises is to replace the radiators with ones made of a different material.


4. Decomposition of organic waste within the system generates gases

Of course, the noise problem is related to the heating circuit and the radiators, not to the DHW circuit. The DHW circuit is open, so it does not tend to accumulate pressure or gases. The opposite occurs with the heating circuit, which, as it works based on pressurised water, accumulates gases and can generate noise, which will be heard quite a lot when the heating is turned on.

Paradoxically, this can sometimes happen even when the installation has just been done, or when some maintenance or repair work has been carried out. When installing or opening the system, organic particles may get into the system, which then decomposes inside the circuit and generate gases and noise. The solution is to wait for the waste to finish decomposing, or to thoroughly clean the circuit.

5. Excess water flow

If you notice that the radiator is noisy after bleeding it, and the noise consists of hissing sounds, you should understand that this is a normal result of the flow of water moving air within the system.

But hissing may be abnormal if you can’t get rid of it by routinely bleeding the radiators. In these cases, the solution may be to reduce the flow of water inside the system, since the normal pressure of your hydraulic system is too high for your radiators.


2 types of normal noise that a radiator can emit

Understanding the types of noise that a radiator can emit will give you indications of the solution to make your heating quieter. Here we list the types of noise that a radiator emits and what they are due to, either before or after a purge.

Creaks when turning on the heating: When the heating is turned on, the increase in pressure inside the circuit produces shocks like a water hammer that are mainly absorbed by the expansion vessel. However, it is normal that as the temperature and pressure rise, the metal of the radiators will creak a little as they go from cold shrinkage to heat expansion.

Metallic blows: This is a frequent occurrence in aluminum radiators, as a result of the chemical reaction between water and aluminum. If it does not reach abnormal levels, it may be that these noises are part of the normal operation of radiators made of this material. If it bothers you too much, maybe you should change radiators.

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