Is your boiler making a strange sound, like a giant, sinister tea kettle? If so, you should call for repairs right away. That sound is a problem called kettling, and it’s a serious threat to the health of your boiler. Let’s take a look at why boiler kettling happens in the first place, and what it can do if you leave it alone for long enough.

Lime Scale

Boiler kettling is, by and large, the result of hard water exposure. Hard water is just water with a high amount of magnesium and calcium particles in it. As the water flows through the boiler system, it deposits small amounts of these minerals on the walls of the pipes. Over time, these deposits grow into lime scale, which restricts the flow of water through parts like the heat exchanger.

This may seem counterintuitive, but most residential boilers are not designed to boil water. As water flow is restricted through the heat exchanger, and water becomes trapped in the part for too long, it will begin to evaporate into steam. Water expands over a thousand times in volume when it evaporates, which puts a huge amount of pressure on the system that it wasn’t designed to handle. That’s where the rumbling sound is coming from: it’s the boiler’s heat exchanger struggling to cope with the rising pressure.


If the kettling isn’t fixed quickly, the heat exchanger could eventually rupture from the pressure. Most boiler systems have measures in place to prevent this from happening, but they will shut down until the problem is fixed. This is why you need to call for repairs as soon as you hear this happening.

Tuckers Air Conditioning, Heating & Plumbing provides boiler repair services throughout Rockville, MD. Call today to schedule an appointment with one of our expert technicians.