My boiler has a kettling noise and water pressure

Written by ian kelly
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My boiler has a kettling noise and water pressure
Extend your boiler's life with scale inhibiters and powerflushing. (Jupiterimages/liquidlibrary/Getty Images)

Kettling is characterised by the sound of boiling, rumbling or knocking coming from your boiler. Since boiling water emits pressurized steam, hot water boilers are designed to heat water to below its boiling point via a heat exchanger. However, after extended use, limescale and waterborne sludge tends to clog heat exchangers. This restricts flow, causing the trapped water to boil and expand; hence the term “kettling.”

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Adding a chemical inhibitor or ‘system restorer’ to the heating system reduces limescale build-up inside the heat exchanger. To accomplish this, a qualified heating engineer either installs a filler loop or specialised radiator to the plumbing. However, this method is designed to retard clogging, rather than to remove heavy encrusted deposits. In addition, harsh chemicals circulating throughout the system can cause pin-hole leaks in radiators if the system is not flushed regularly.

Scale Inhibitor

Adding a scale inhibitor combines two effective technologies in one. A magnetic bar in the device induces single polarity into the water, causing magnesium and calcium particles to adopt the same polarity. The particles then repel each other, preventing limescale from forming. Parallel zinc plates encased in a copper tube installed downstream of the magnet enhances the single polarity effect even further. As an added benefit, the zinc plates release minute particles that prevent air bubbles from forming, thereby preventing corrosion.


In powerflushing, a heating engineer drains the system and connects a high velocity, low pressure powerflush machine to the circuit. The machine then pumps neutralising chemicals through the system. This loosens limescale and flushes out debris. Periodic powerflushing increases efficiency, prolongs system and boiler life, speeds up radiator heating times and reduces your gas bills.


Unlike domestic hot water boilers, steam boilers are designed to cope with high pressure. In addition to reducing the life of your boiler, a clogged heat exchanger degrades boiler efficiency; therefore, rectifying the condition as soon as it arises is a cost-effective solution in the long run.

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