Heating System Noises Explained

Picture: © Irena Maslova / Shutterstock.com

With cooler weather rolling in, the time has come once again to ready your heating system for a season of work. But starting up your system may have you hearing noises that prompt questions of malfunction.  

Faults, such as air in the hydraulics, can cause the heating system to make noises. Whether gurgling, gushing noises, whistling or humming, the most common heating noises can be distinguished from each other quite easily. A heating contractor can identify the problem from the noise or at least narrow down the possible causes.  Today we will explore which sounds are normal and those that could mean it's time to call your heating professional for service.

What you can do yourself about heating system noises

Noticeable heating noises can indicate that individual components of the heating system are not set correctly or are not functioning properly. At worst, there is a fault that should be repaired quickly. However, flow noises and water noises from the heating system are normal with in certain parameters. After all, there is hot water running through the pipes. Therefore, it is important to assess whether there is a problem at all. If so, the expertise of a heating engineer is essential. Ideally, system owners should first ask the heating contractor that installed the heating system.

What type of noises are coming from the heating system?

So that you can distinguish harmless operating noises from critical ones, we have listed the most common heating noises in the following section. The associated causes are based on experience. The information is not guaranteed to be accurate in every case. If in doubt, consult a heating contractor who will listen to the noise themselves.

In case of these or similar water noises, there is probably air in the heating system. The radiator should be bled. You can easily do this yourself, even without a heating engineer. All you need for this is a vessel to catch water, a rag or cloth, and a bleed key, which can be bought at a DIY shop or a specialist shop. Once you have gathered everything, simply follow the step-by-step instructions below to bleed your radiators.

Step by step: bleeding the heating system correctly

1.  Switch off the heating circuit pump
2.  Open all thermostats
3.  Place a cloth underneath or wrap it around
4.  Position the bleed key on the air vent valve (usually on the side opposite the thermostat) and hold the vessel under it
5.  Turn slowly and let the air escape
6.  As soon as water escapes, close the bleed valve
7.  Restart the heating circuit pump
8.  Ensure that the water pressure is sufficient: if necessary, contact a heating contractor who will top up the system in accordance with Energy Conservation Standards


If there is noticeable gushing noise from the heating system, the circulation pump is most likely set too high. This means that a lot of water is flowing through the system. The gushing noise in the pipes is correspondingly louder. The appropriate setting differs depending on the demand of the heating system. Therefore, a contractor should always be contacted.

Have you carried out renovation work? If the heat demand of your house has changed as a result, the heating contractor will usually carry out hydronic balancing. During hydronic balancing, the heating engineer checks the entire heating system to ensure that the heat distribution in the house is correct. This can also eliminate any annoying gushing noise.

A knocking or cracking noise in radiators or in the wall can initially cause concern for a homeowner, however the cause can often be traced back to the brackets for the hot water pipes. Hot water causes pipes tend to expand. Too-tight wall brackets can cause eerie noises. In this case, a heating contractor should replace the brackets and/or re-insulate the water pipes.

The heating system may also make cracking noises if the pipes are not installed free of tension. The often difficult task of identifying the relevant location should be undertaken by a heating contractor. Ideally, they will also know the sustainable and effective solution to the "crackly" problem.

If the heating system makes knocking noises, a missing or improperly adjusted overflow valve may also be the cause. In older systems, it may be responsible for excessive pressure in the heating system. Call in a heating contractor. They will take a closer look at the valve, which is located above the circulation pump, and readjust it if necessary.

A humming noise from the heating system often occurs directly at the thermostatic radiator valve. In this case, the heating circuit pump is probably set too high and produces the humming noises after the thermostat is turned up. If the heating system is well adjusted by hydronic balancing but still hums, this may be due to an old heating circuit pump. A heating contractor will determine the exact cause and replace or clean outdated or contaminated components.

Technical faults cause noise – and costs!

If heating noises alone are just annoying, the underlying technical faults can cause real costs. A faulty or improperly adjusted heating system consumes more energy than necessary. This not only drives up heating costs, but also wastes resources. Therefore, possible causes should be checked and eliminated in any case.

When the heating makes no noise at all

Soft operating noises are part of every heating system. After all, water is moving around a heating circuit. Even switching on a burner is not completely silent. If, for example, your gas boiler remains completely silent, this may indicate that the system is not running or cannot be started up. This becomes apparent when the heating does not get warm. As a rule, the system also reports a corresponding fault on the display. In any case, you should definitely contact a heating contractor so that the heating system can be checked and repaired.


Tips for tenants when heating noises occur

For you as a tenant, most of the measures to stop heating noise are probably not feasible. In most rented apartments, access to the boiler is not guaranteed. Therefore, as a tenant, it is best to contact the landlord if the aforementioned heating noises occur. In order to remedy the causes, the latter in turn rely on the observations, logs and documentation provided by their tenants. Access to the apartment for installers should also be possible in agreement with the tenant.

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