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Plumbing in the Home/Humming after toilet flush



I have 3 toilets in my house.  The toilet upstairs has a FlushMate system installed in it and it's more than 12 years old.  Downstairs, I changed the flush valve and flapper about 4 months ago in the 2nd bathroom to a FluidMaster.  Up to that point, all 3 toilets were working fine with no hum.About a month ago, I changed the flush valve and flapper on the 3rd toilet to a FluidMaster also because it was leaking.  About 2 weeks ago, I started hearing a humming noise coming out from the 2nd bathroom, evert time I flushed any of the toilets.  the hum would start as soon as the tank would start refilling and stop when the tank was full.

I read many of the postings online for troubleshooting ideas.  When I turned the valve cap counterclockwise to one of the valves, I could get the humming to stop temporarily.  This only worked in one bathroom though, not the other.  When I stopped the water from filling the tank by raising the floater, that would stop the hum temporarily also.  Opening nearby faucets didn't help.  Reducing the flow of water to the tank helped but also temporarily.  Temporarily means for a few flushes only.  

Please advise what else I could do to solve the humming problem permanently.



ANSWER: Hello Elie,
The Fluidmasters use a diaphragm type water control valve. There is either some debris on the seat of the valve preventing the diaphragm from fully seating or the water flow to that toilet is too low and is not keeping the valve diaphragm open far enough while the toilet is filling. It is fluttering like the reed on a musical instrument as the water passes by and causing this hum you are hearing.

The Fluidmaster can be taken apart and cleaned if needed. Low water flow is another issue. That could be old, plugged up pipes reducing the water flow or a clogged shut off valve at the wall. This can be verified by turning the water off at the shut off under the toilet, disconnecting the supply line under the toilet tank and pointing it into a bucket while turning the water on.
Good Luck,

---------- FOLLOW-UP ----------

QUESTION: Thank you Dana for the quick advice.  I will check out the Fluidmaster for debris.  As to water pressure, I already checked it and it was fine.  In fact, by shutting the supply line halfway, I was able to reduce the humming considerably to a faint and brief hum (not gone entirely).  

What I don't understand is why do I hear the humming come out of toilet #2 when I flush toilet #3. What is even more strange is that when I flush toilet #2 a second and third time, I don't hear any humming out of any toilet.  It eventually comes back.  


It is possible that the pressure is too high. 80 psi is as high as plumbing components are designed to handle.  As for the sound location, hard to say. Water is an excellent transmitter of sound. When you flush one toilet, the pressure drops in the system just a bit and that may be enough to allow the #2 toilet to by-pass a bit of water, causing the diaphragm to hum.  Try setting the float a bit lower in that toilet to provide a more positive shut off.
If all else fails, replace that Fluidmaster.

NOTE: there is a big difference between pressure and flow rate. If you were to have an 80 psi static pressure, a 1/4 inch pipe would flow a lot less gallons per minute than a 1/2 or 3/4 inch pipe at the same pressure.  Most people complain about lack of pressure when they really mean lack of flow rate.

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Dana Bostick


Pretty much any residential plumbing questions. For "item specific" details such as a specific model of fixture, I will need to research and there may not be any useful information available. Note: I live and work in Southern California. We do not, as a rule, use hot water or steam heating systems, oil fired boilers or private water wells so my knowledge in those areas is pretty limited. There are others here on AllExerts that can probably answer those questions better.


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