Humming Toilet Tank Fill Valve

The Case of the Haunting Humming Sound in our Home’s Plumbing System

By Mark J. Donovan




Over the past couple of weeks we’ve been hearing this humming sound in our home’s plumbing system. Today I isolated the problem down to a humming toilet tank fill valve in our downstairs bathroom.

When I first started hearing this humming noise I thought it had to do with a plumbing supply line, but I was not totally convinced of this due to the frequency of the particular hum. It was a very low frequency hum that crescendoed in volume from a low whisper to a loud reverberating sound, before fading away again.

The sound was very audible on both floors of the home. After a week of trying to figure out what was causing the sound I discovered our downstairs toilet was the culprit.

After thinking about this situation a bit more, I began to contemplate that there was something caught in the vent stack that was causing the sound when the toilet was flushed. Again, the sound was so deep and hollow sounding I concluded it could not have been the cold water supply line.

On the other hand, I was baffled on why only the toilet would cause this humming sound since all of the plumbing fixtures are in effect tied to the plumbing vent stack.

Today, however, I discovered I was partially wrong. When I flushed the toilet I lifted the lid on the toilet tank and watched and listened as the toilet tank filled. When the water reached the appropriate height to shut off, the toilet began to resonate with the crescendoing hum.

How to fix a humming toilet tank fill valve.

What I observed was that as the toilet tank fill valve began to shut off, caused by the height of the float ball, the arm and float ball assembly began to vibrate.

As it increased in vibration the toilet tank began to hum in a low frequency growl. The hum increased in volume until the toilet tank fill valve began to finally close off the flow of water to the tank. As the tank fill valve finally closed off the hum faded away.

So in the end the hum was associated with the supply line, and more specifically the toilet tank fill valve shutting off. As the fill valve shut off, the float ball and arm began to vibrate and resonate within the toilet tank, and thus caused the low pitched hum.

To resolve this problem I adjusted the small screw setting on top of the toilet tank fill valve. The hum seems to have now disappeared. If it reoccurs I plan to replace the toilet tank fill valve assembly altogether.

So if you ever hear a loud low moaning sound in your plumbing system check the toilets. You may have a toilet fill valve that is in need of repair or replacement.

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