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Reducing Boiler Noise

What causes boiler noise?

Boiler noise is usually the result of limescale deposition within the heat exchanger of a 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. Other sediment-forming debris such as sand and brick dust entering the system during installation can also become part of the hardened deposit. Local water conditions also play an important part, particularly the scale-forming solids dissolved in the supply water.

Boiler noise is directly related to the rapid condensation or implosion of steam in water. Localized boiling develops on the surface of the deposit, and small steam bubbles are created that make a rattling noise as they leave the surface and travel around the system.

When installed into existing systems, new boilers can become excessively fouled soon afterwards by oxide sludge present in the system water. Replacing a boiler can disturb soft sludge and loosen sediment in other parts of the system, causing it to be transported by the system water and re-deposited in the new heat exchanger.

The same phenomenon can occur as a result of circulator replacement if flow rates change. The risk of sediment and sludge deposition in new boilers can be avoided by cleaning the system as part of the installation process. Guidance on correct cleaning and treatment can be found in BS 7593:2006 Code of Practice for Treatment of Water in Domestic Hot Water Central Heating Systems.

What should be done?

Fernox DS40 System Cleaner selectively dissolves oxide sludge without attacking metals commonly found in central heating systems. However this acid-based cleaner should only be used in new installations.

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 can be substantially improved, however, by dispersing the sludge with Fernox Cleaner F3 or Powerflushing Cleaner F5 , followed by power flushing with plain water.

After removing all soft sludge from older installations separate boiler de-scaling may be helpful. In order to do this, the radiators should be isolated after which the system can be descaled over a period - up to 24 hours.

This should be followed by rinsing with plain water and neutralizing to passivate the surfaces within the system. Fernox DS40 System Cleaner and Neutraliser can be used in this process.

After cleaning, the entire system should be re-treated using Fernox Protector F1 to eliminate the causes of boiler noise.