It’s pretty likely that you’ve been around your boiler a few times while it’s been operating. Most of the time, a boiler is no more noisy than any other heating system. If you hear a deep rumbling noise coming from your boiler when it’s on, however, it’s a sign that something is wrong. This rumbling sound is part of an issue called “kettling,” called such because it essentially makes your boiler into a giant tea kettle. Here, we’ll examine what causes kettling, and why you should have it looked at as soon as possible.


Hard water is the term for water with a much higher concentration of minerals in it than normal. It is common throughout the Midwest, though it can affect some areas on the coasts as well. This kind of water is especially hard on pipes and faucets, causing calcification and rust. In a boiler, however, the biggest problem is the formation of lime scale.


Over years of flowing through your boiler, hard water will deposit small amounts of the minerals within it on the inside walls of the heat exchanger. Eventually, these minerals will build into scaly deposits that restrict and even block the flow of water through the heat exchanger.

As the water spends more time in the heat exchanger, due to the restricted flow, it begins to evaporate into steam. This causes a massive increase in pressure within the heat exchanger, causing the deep rumbling noise that is characteristic of kettling.


Kettling is very unhealthy for your system, and should be addressed immediately. Kettling can prevent your boiler from adequately heating the house, by restricting its ability to distribute enough hot water. The increased pressure from the water expanding can also wear out your heat exchanger much faster than normal, causing leaks to occur. It is commonly thought that, due to the sound and the obvious pressure concerns, boilers that are left kettling for too long may explode. Modern boilers have multiple safety measures installed to prevent this from happening, so it isn’t anything to worry about.

If you’re having problems with your boiler, call BZ Dependable Plumbing & Heating, Inc. Our heating professionals cover all of Englewood.

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