Why a Boiler makes noise?

Your time at home can be very frustrating if your boiler makes a noise.

Boilers make noise for many reasons. Boiler engineers often refer to the noise as ‘kettling’. They usually divide the causes for it into two groups, chemical and mechanical.

Chemical factors

A foaming system can lead to overheating. The chemical water reduces contact between the water and the heat exchange. The foam which is responsible for this overheating is mostly due to residuals, suspended solids, or other contamination. There have been cases in the past where people have added washing up liquid into the central heating system as they have been informed that washing up liquid reduces the boilers noise. This is incorrect. In fact, washing up liquid produces foam which causes one of the main reasons for the boiler noise. The chemicals also produce large amounts of corrosive chloride.


Boilers make noise because deposits insulate and partial insulation of the heat exchange surface can cause uneven heating. In central heating systems, such deposits will likely be corrosion debris or thin limescale deposits. In hard water areas, limescale forms in the hottest part of the system. The heat exchange surface generates thin and patchy deposits of scale. Subsequently, an increase in heat transfer temperatures can lead to kettling.

Mechanical factors


Boilers make noise because a badly installed high power boiler in a small heating system can lead to overheating. This is because the heat exchange is unable to remove all the excessive heat. This can cause boiling and a loud noise.

Flow Rate

A wrong flow rate can prevent the heat dissipation in the boiler.  This can cause boiling in the boiler and subsequently loud noises.

Boiler Temperature

There’s a danger that the boiler’s thermostat is not working. Please check to see if it changes with time. If you notice that the thermostat doesn’t change with time then replace it to make sure that there’s no risk of overheating.

Boiler Design

If there’s a thermostat on every radiator valve, this can cause a boiler to cycle quickly and overheat. This can contribute to the boiler making noises that are more loud than usual. Furthermore, if the pipes are of the wrong size or fit, this can cause imbalances which causes the boiler to make loud noises.

Mistakes in the boiler mold

Any errors in the casting can result in overheating.

Firstly, shut down the power to the boiler

The noise is often due to ‘kettling’, often when the pilot light first ignites.

Air may be trapped inside the boiler

Locate the air bleed screw on the pipework around the cylinder. This will be about 10cm of piping that has a screw that you can bleed at the top.


Check that you have enough water going inside the feed and expansion tank. This is normally found in your loft. It might be full with sludge.

Removing the sediment by flushing the system might sort the problem. If you know you have a pressure system, check the pressure is at the right level. Or if you know you have an open-vented system, check the in-feed to the expansion tank. However, please first consult with your boiler’s installer. A study by Gas Safe Register states that one in ten boilers are not safely installed. If your boiler is making funny noises do not try to fix the boiler yourself.  There is a high risk and danger that you will thaw and break the condensate pipe, which is easy to access. If your boiler was installed by us then please do get in contact as soon as possible, otherwise we can replace your old inefficient boiler with an A rated boiler from £19.99 per month.

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