toilet
Mansfield 1.6 Toilet. Relatively recent (<3 years old) Korky fill. Hissing noises. Water level stable.
So, I replaced the drain stack with a new one, new gasket, bolts, etc). Put it all back together, and I'm right back where I started. If I'm hearing watery noises from the Korky unit, where is the water going, if the level in the tank does not go up and over the overflow in the drain stack? Should I just replace the fill at this point? Needless to say, no sign of water outside the toilet.
The most common problem that causes the symptoms you describe is a slow leak around the flapper. A very small amount of water drains into the bowl over time, lowers the tank level a slight amount and activates the float valve of a couple of seconds to refill the tank. What you should do before getting carried away dissecting the fill valve, is to check the flapper, clean it and it's seat well and be sure it is centered on the drain. If there are any signs of wear or cracks around the edges, replace it. Monitor the tank level between phantom fills, does it change at all? The second thing is to slightly lower the float so the water fills to apx 1/2 inch below the fill mark. This will eliminate the possibility that you may be losing water over the overflow, and tripping the fill valve.
These checks are simple, cheap and often solve a very common problem. Good Luck.
I think @Tester101 has asked the pertinent question: Is the fill valve height adjustable? It is. You need to adjust its height:
Best Answer
There should be a tube coming from the ballcock valve (Korky unit) going to the overflow pipe with a clip holding it onto the edge of the pipe. The purpose of that is to run some water down directly to the bowl after the flapper closes in order to refill the bowl (and help take care of "Klingons" on the side). I have found Korky fill valves to be especially susceptible to leaking through to that bowl refill tube continuously. The water runs along the side of the overflow pipe, so it's hard to see. You don't see anything going over the top of the overflow pipe and if you put dye in the tank you don't see it leaking. But if you pull that bowl refill tube off of the clip, you will see a small stream or drip of water coming out.