What Causes a Heating Boiler to Make Noise When Firing?

Hot-water heating boilers normally are unobtrusive and quiet. They usually heat your home quietly all winter, which means you hardly know a boiler is functioning, however, as hot-water boilers era, they can start making a rumbling, burbling, percolating sound once the burner is firing. This “kettling” noise might turn out to be quite loud during operation but subsides shortly after the burner shuts off.

Mineral Deposits

A hot-water heating boiler is designed to function in a temperature just below water’s boiling point, typically around 180 degrees Fahrenheit. In areas with hard water, mineral deposits may form on the boiler tubes. This is the usual source of boiler kettling. When water is heated in the boiler, the calcium salts dissolved in the water form lime scale on the boiler’s heat exchange tubes. The scale layer raises the temperature required for heat exchange, and the rough surface of the lime scale causes hot spots above water’s boiling point, creating air bubbles in the boiler water. As the bubbles rise into cooler water, they fall noisily. The creation and collapse of the air bubbles causes the kettling noise. The deposits decrease heating efficiency and may also increase fuel consumption. .

Size Mismatch

Mineral deposits are the most frequent cause of hot-water boiler kettling, but there are some other causes that sometimes happen. These causes include an incorrectly rated burner that’s too large for your boiler size. The outsized burner can overheat the boiler and make localized boiling. A circulating pump that’s too small for the system can cause flow rate through the system that’s too slow to dissipate the burner’s heat, resulting in boiling as well as the kettling noise.

System Flaws

A malfunctioning boiler water heater may cause the burner to function too much, resulting in overheating and boiling. Bad system design with pipes mistakenly sized may impede water flow, resulting in excessive boiler boiling and temperature. Contaminants in the boiler water may result in foaming, which reduces contact between the boiler tubes as well as also the water, resulting in overheating and bubbling. Air trapped in the system can create noise.

Boiler Treatment

Correcting boiler noise is a project for a heating technician. If the technician has checked for trapped air and removed burners, thermostat, pumps and other mechanical causes for boiler noise, he can try out a chemical descaling of this boiler. This involves shutting down the system and letting it cool. The next step is adding a commercial descaling chemical, restarting the boiler as well as allowing the substance to work for many days. The final step is to flush the boiler to remove the dissolved scale, then refill the boiler with new water.

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