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What’s That Sound? Troubleshooting Mechanical Room Noises

Mechanical boiler rooms usually have numerous noises going on at all times. When you hear a noise that isn’t part of the normal symphony, it’s important to try to figure out what’s going on with your boiler system.

If you hear a loud humming noise coming from your boiler, you might have a seized part on your pump. Often, the best sign of a seized pump is if it’s hot to the touch. A normal pump would be warm, but a seized pump will be hot. To fix this issue, your pump might need to be thoroughly cleaned.

Hissing often indicates your system is overheating, likely due to an air pressure issue. Like the case above, your system might need to be cleaned to flush out any build-up and debris that could have settled over time. Before cleaning your whole system, you should try releasing some of the air through the bleed screw and then seal it back up to see if that fixes the hissing sound.


A knocking noise can be caused by limescale or sludge build-up on different parts of your boiler. From there, your system can develop hot spots. When water reaches those spots and turns to steam, the air expands and makes a knocking sound.

A clanging noise could be due to a loss of boiler pressure. Sometimes this could be because you need to increase the water flow rate, or it could be because of a leak you need to find and repair.

A banging noise could be caused by airlock in your boiler pump, which you will typically notice soon after you turn the boiler on. To fix this, you can loosen the bleed screw to the pump which will slowly release air. Be sure to tighten the screw back when you’re finished bleeding the system.

Take a look at the video above to see how steam can make such loud noises in a heating system.

As we’ve seen above, sometimes the strange noises in your boiler system can be caused by grime build up and a routine system cleaning can take care of most of those issues. This method isn’t always the solution, and if your problem noises persist you should contact your local boiler expert at Hoffman Hyronics for a solution geared toward you.

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