Kettling is caused by the boiler being exposed to hard water over a long period of time. Hard water is water that has a very high mineral content. It is common to certain geographical areas such as Cork, Waterford, Dublin and Galway. As the hard water flows through the boiler, it deposits small amounts of minerals on the walls of the pipes. This is especially problematic for the heat exchanger. After years of this kind of buildup, the mineral deposits can become large enough to actually restrict or block the flow of water through the heat exchanger. This causes water to actually boil in the pipe, expanding into steam and putting enormous pressure on the heat exchanger. This increased pressure is what causes the rumbling sound associated with kettling.
There may be some other causes for kettling sounds,e.g. the boiler has been installed inappropriately or because it has incorrect settings. A faulty boiler thermostat can cause the boiler to overheat signalling that the thermostat needs to be replaced. A pump that has become stuck or needs replacing can also produce a very loud banging noise.Is Kettling Dangerous?
The main danger of kettling is the increased wear and tear, which will cause your boiler to wear out faster and require replacement. Kettling puts various parts of the boiler, mainly the heat exchanger, under pressure that can quickly wear out these vital parts. . If the heat exchanger is forced to operate this way for a long period of time, it could rupture, causing water damage to the boiler and surrounding area. Most boilers have safety measures that will shut down the system long before that happens, alternatively an RGI (registered gas installer) may shut down the boiler during service or repair.
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