Here is the inside of our toilet tank:

enter image description here

Not sure what that "yellow thing" on the top is, but I believe that's the main culprit to focus on. For now, I'll call it the yellow thing.

When the water supply is running full bore, water seems to be leaking out of the top of that yellow thing, where the "cap" (or whatever it is) is. This causes the toilet to sound like its "running continuously", or refilling continuously. Meaning, its never quiet and just constantly makes that sound that a toilet makes when its tank is refilling with water.

So a few days ago I shut off that water supply line, just because the running noise was driving us crazy and I didn't really have any time to look into the issue.

Despite the fact that I shut the water supply off, we've still been able to use the toilet in those last few days! Not sure if that's normal, but is not what I was expecting! However, as you can see, the water line is pretty low. So perhaps we just haven't flushed it enough times (since it's been turned off) to fully drain it.

But now that the water supply line is shut off, and the water in the tank is low, the bottom of that yellow thing drips constantly and is driving us crazy.

Clearly we have at least 1 leak here. I'm worried that we have a leak not only in that yellow thing (again, whatever it is) but perhaps also in our water supply line valve. How else would water be constantly dripping into the tank when the supply line is shut off?

Either way, any ideas as to what is going on here and how to fix our toilet? The desired end result is normal toilet functioning, with the supply line turned off and with it not "running continuously". Thanks in advance!

3 Answers 3


Sounds like you need to replace the flush valve and possibly the shut off valve.

If you believe you have the water shut off, and you still have a drip, then the shutoff valve is corroded enough to jam before it is fully off.

The flush valve is pretty obviously malfunctioning.

Replace both of these and you should be back to normal.

Good luck!

  • Thanks @ArchonOSX (+1) - (1) does this mean that my "yellow thing" is actually what you are calling the "flush valve"? Also (2) when you say "the shutoff valve is corroded enough to jam", what do you mean? Why would corrosion cause a valve to jam? Thanks again!
    – smeeb
    May 4, 2016 at 11:22
  • Also, Googling images of "toilet flush valve" make it seem like the flush valve is the rubber gasket/valve at the bottom of the tank. But that's not what appears to be leaking. Again, water seems to be pouring out of the "yelllow thing"...thoughts?
    – smeeb
    May 4, 2016 at 11:51
  • 1
    The shutoff valve will be the faucet that shuts off the water supply to the toilet. They are often on the wall near the floor by the back of the toilet. These faucets are rarely used and often after years of being open there will be mineral deposits and buildup inside the faucet. When you come to shut it off it will not fully close due to these deposits inside the faucet. Many faucets also have internal rubber seals and these degrade after years if sitting in chlorinated water or water with high mineral content. In any case if this is in your faucet it needs replacement.
    – Michael Karas
    May 4, 2016 at 12:44
  • 1
    When @ArchonOSX was referring to the flush valve he meant the water tank filler shut off valve. These usually operate on some type of float mechanism rises when the water tank fills and shuts off the water flow into the tank when it gets to a certain level. The fact that it keeps running as you reported indicates that this part is not functioning properly. Thus it is recommended for replacement. The filler valve assembly is usually not that spendy. In all likelyhood that yellow thing is part of this assembly and will come completely out when you deploy a replacement.
    – Michael Karas
    May 4, 2016 at 12:50
  • 1
    The black rubbery thing in the bottom that lets the water tank drain down into the toilet stool proper is normally called a flapper valve. While you go about replacing parts in the water tank it is recommended to replace that flapper too. In my experience those only last 2-3 years at best. You can tell if the part is failing if when you rub your fingers on it if they come away with a black residue which is from the rubber part degrading due to chlorine and minerals in the water.
    – Michael Karas
    May 4, 2016 at 12:55

The yellow thing is the fill valve. It is the thing the water actually enters the tank through. There are few different ways they can work but in your example the large yellow body probably houses a float that closes the valve once the water level reaches the appropriate height.

The large, black, vertical tube is the overflow tube and at its base is flap.

The small black tube from the fill valve to the overflow tube is to direct little bit of water into the bowl and ensure it is complete filled.

This as a diagram of a toilet with the 'old' style float, but the principle is pretty much same.

enter image description here MIT.edu

Your toilet could be running constantly for a number of reasons.

1) The float needs adjustment. The float could be out of adjustment and now 'full' is above the overflow tub. The float never quite gets to the level it needs to so the water keeps filling but it spill over the top of tube and into the bowl.

2) The flap is old, stiff and maybe cracked. This allows water past the flap and into the bowl. The valve opens to fill the toilet.

3) Sediment from the water line has managed to lodge itself in the valve, always holding it open a tiny bit. This can eventually free itself though use but is hard to clean out without taking the thing apart. I had this happen for a while on a house after I shut the water supply off, drained the house and turned it back on.

Finally. If your toilet is still running even with the supply shut off. The supply shutoff may be damaged. I hate to ask the obvious but did you turn it the right way? It may have not been opened all the way to begin with, and you just opened it all the way.

But a fill valve kit and shutoff valve is not terrible expensive and a novice should be able to do it in an hour to hour and half. You might need to get a good wrench or pipe wrench, and be able to turn off the water to your house.

Plus you get the experience of doing some basic DIY and save the cost of a plumber's hour price.


Is your toilet stool broken?

There seems to be a serious crack as indicated in this snip:

enter image description here

If this is a crack as it appears it may be wise to replace the toilet seat as well. Cracks in the toilet seat can lead to water leakage down under the toilet and into the building structure below. This is something to be concerned about as wet wood invites mold and rotting.

  • Thanks @Michael Karas (+1) - fortunately this is just debris (likely a plastic needle from a fake pine tree that hangs above the toilet). But I appreciate you bringing this to my attention and it definitely taught me something!
    – smeeb
    May 4, 2016 at 13:20
  • Yes, definitely check this - in the renovation-project-cottage I recently bought, the only thing preventing the toilet from falling through the water-damaged & rotted floor was the ancient cast-iron drain pipe it was resting on...
    – brhans
    May 4, 2016 at 13:21

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