Boiler Kettling: Why is the boiler making strange noises?

Boiler kettling is usually the result of overheating due to internal limescale or corrosion, or insufficient flow of water. Boiler kettling is often used to refer to any kind of unwanted boiler noises, like banging, rumbling or whistling.

Most boilers aren’t silent. They usually make some sound as part of their normal operation. For example, you may usually hear the whirr of the pump or the hum of a fan. However, in some cases, the sounds are clearly out of the ordinary. This article will help you understand what’s going on if you have a noisy boiler.

Boiler kettling explained

  1. Over time, limescale forms in the boiler’s heat exchanger, much in the same way as it forms over the element in your kettle.
  2. As the water is heated, bubbles of air become trapped underneath the limescale. The sound of a kettling boiler is the result of these air bubbles expanding and bursting.

This process is exactly why your kettle makes that distinctive rushing sound shortly before the water boils. As you might expect, boilers in hard water areas are more prone to kettling.

Before spending a couple of thousand pounds on a new boiler, one solution may be to add descaling chemicals to the system, letting them act slowly, and then draining or powerflushing them out at a later date.

Other reasons for boiler kettling

Flow rate

Poor water flow rate is another possible reason for boiler kettling. If water flows through the heat exchanger too slowly, it picks up too much heat, and becomes hotter than it should be. This can also result in bubbling or boiling sounds. The word boiler isn’t a particularly accurate term, since the water in a boiler should never actually boil.

A bad boiler installation can also cause poor flow rates and encourage the build-up of limescale and sludge. Once again, these will restrict the flow of water through the heat exchanger. A power flush may resolve the issue. After powerflushing, central heating inhibitor and descaling chemicals should be added to the system to prevent the problem from occurring again.

Poor flow rates can also be caused by a faulty pump, or one whose speed setting is too low.

Blocked condensate pipe

A blocked or frozen condensate pipe may cause condensate to collect in the sump, making a bubbling or gurgling sound before eventually triggering a fault code and stopping the boiler from working. For more information on this fault, see the following page: Frozen condensate pipe: how to fix

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