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.
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.
You have water leaking slowly into the bowl. This can be a warped flapper seat, build up on seating surface, or worn valve seat.
To verify, mark the water level in the tank with a pencil and turn off the water valve. Come back in 30 minutes and see that the water level has changed.
To fix:
Korky will also help you troubleshoot by calling them at (800) 523-83553
Hissing means water movement. Period. It's a leak.
In valves, there are two kinds of leaks. Leaks external to the valve - i.e. puddles in places water does not belong. And leaks through the valve -- i.e. water flows in correct places, but the valve refuses to shut off all the way.
In a sink/tub, it's easy to recognize the second type -- the faucet keeps dripping. But it's hard in a toilet, because toilets stay wet, and there's nowhere to observe water movement.
We know for a fact that you have a leak; now it boils down to "where". A toilet has 2 valves: the huge valve that empties the tank into the bowl; and the refill/float valve that refills the bowl.
Pop off the tank lid. The tallest thing in there will be the fill/float valve. The second tallest will be a simple tube sticking out. It's like a "glory hole" for a reservoir; it's an emergency spillway in case the refill valve sticks open. Normally the water should be below that. If the water is overtopping the overflow valve, the leak is in the refill valve.
Otherwise most likely the leak is in the flapper valve; however you usually expect intermittent action of the refill valve in that case. The drain would be continuous, but the refill valve has some hysteresis/slop: it fills to point X and shuts off, but it won't reopen until the level falls somewhat. So it'd be off for 3 minutes, on for 15 seconds, repeat.
Refill valves and flapper valves are different items, but each is around $10US.
