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What is Kettling in Boilers?

The sound of a kettle boiling is usually comforting but when that sound is coming from you boiler it can be rather alarming. The similar sound to a kettle boiling coming from your boiler could be down to something called kettling.

A boiler operates by heating hot water via a heat exchanger. In areas of hard water, lime scale deposits build up on the heat exchanger and restrict the flow of water. Hard water used by boilers has a higher proportion of calcium salts (lime) in it than soft water. As the water heats, these salts become insoluble in the water and settle at the bottom of the container in which they were heated. When the water flow is restricted as it is trapped in the heat exchanger it becomes too hot and starts to steam, boil and therefore expand. This is what causes the noise. It is also possible for other debris from the system, known as sludge, to collect on and around the heat exchanger causing the same problem.

There may be some other causes for kettling sounds, such as that the boiler has been installed inappropriately or because it has incorrect settings. A faulty boiler thermostat causes the boiler to overheat, the only way to deal with this is to replace the boiler thermostat. A boiler which is too large in view of the total heating space also makes banging noises. Finally a pump that has become stuck or needs replacing can also produce a very loud banging noise.

Some of our customers worry that boilers may explode because of kettling, but don’t panic. Boilers have numerous safety controls that should kick in and lock the boiler out (to turn it off) before any such problem occurs. A combi boiler is able to combat the fact that water expands 1600 times when turning into steam by having a pressure relief valve. A traditional boiler will make use of the expansion cistern which is normally in the loft.

It is very important for a plumber to establish the cause of a boiler locking out, diagnose the heat exchanger at fault, and remedy the problem.

Kettling can easily be cured and prevented from reoccurring. Ways you can cure and prevent kettling:

  • Replace the heat exchanger
  • Powerflush the system
  • Fit a Magnetic and Electrolytic Scale Inhibitor
  • All liquid inhibitor to the system
  • Fit a Magnabooster
  • Flush the system through and Powerflush

If you are concerned about any noises your boiler is making give us a call and we will strive to quickly and efficiently diagnose and fix the problem.

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