What causes boiler noise?

The most common cause of boiler noise, also known as ‘kettling’, is limescale deposition within the heat exchanger of the boiler. This condition is worsened if magnetite is also present in the system, as this combines with the limescale to form a much harder deposit.

As deposits are good insulators, it is the partial insulation of the heat exchanger surface that can cause uneven heating and the rattling noise you hear. Other deposits can include oxide sludge, sand and brick dust. Replacing a boiler can disturb soft sludge and loosen sediment in other parts of the system, causing these contaminants to be transported by the system water and re-deposited in the heat exchanger. The same issue can occur as a result of circulator replacement if flow rates change.

Boiler noises could also be due to mechanical problems within the central heating system. This could include incorrect gas burner pressure or flow rate, faulty thermostat, or casting faults.

Where is the noise coming from?

If you have checked your boiler for mechanical faults and have found everything to be in good working order then you can deduce that your noisy boiler is due to limescale deposits on the heat exchanger.

In this case, the noise you hear is directly related to the rapid condensation or implosion of steam in water.  Localised boiling develops on the surface of the limescale deposit, which creates small steam bubbles. It is this movement of bubbles that creates the rattling noise as it leaves the deposit surface and travels around the central heating system.

What are the solutions?

Fernox Boiler Noise Silencer F2 can be used to reduce the size of steam and air bubbles which form on a heat exchanger. This is achieved by reducing the surface tension of the system water which means only small bubbles are able to form and therefore the associated noise is significantly lessened. However, this product will not solve the underlying causes and therefore a full system clean should be performed at the earliest opportunity.

In systems that are less than 10 years old, an acid based cleaner can be used to remove deposits in the system. Fernox DS40 System Cleaner selectively dissolves scale deposits without attacking the metals commonly found in central heating systems.

Older systems that have been untreated for periods of time may have existing leaks that are temporarily plugged with corrosion debris. Installations with a history of radiator corrosion failures should not be acid cleansed, as other radiators are likely to have deep corrosion pits or complete perforations.

Older installations however, can be improved by dispersing the build-up.  We recommend neutral pH cleaners Fernox Cleaner F3 or Fernox Powerflushing Cleaner F5, followed by flushing with plain water. This will remove sludge deposits.

Once sludge has been removed from older installations, it is recommended that descaling is performed on a small circuit, including the boiler.  In order to do this, all the radiators should be isolated after which the system can be descaled using acid cleaner Fernox DS40 System Cleaner. This should then be neutralised using Fernox System Neutraliser for safe disposal to a foul drain. After cleaning, the entire system should be flushed with plain water before treating with Fernox Protector F1 to eliminate the causes of a noisy boiler.