Toilet spontaneously hisses

[LiLi]

For the last few months, my American standard toilet has been making a very loud hissing noise, on its own, about every 30-45 minutes. I paid close attention to it this weekend, and the water level sinks about an inch, the loud hissing sound occurs as it refills, and the float pops back up. Then it repeats. I drained the tank and cleaned the flapper with scotch-brite, and the flapper seemed to be in good shape (no cracks or discolouration), but the problem hasn't resolved, and I am totally at the end of my (non-existent!) skill! I turned the water to the toilet off yesterday to give myself some peace (from the sound and the from the water bill), but what should I do next? If it helps, I had the wax seal replaced recently, but before that happened, I couldn't use the toilet for two months. I do know that the toilet still had a great deal of water in it (tank and bowl) when it was finally repaired. Please help!

Thank you so much!

 

[havasu]

Did you scrub the underside of the flapper (on the porcelain) ? This is where it needs to be perfectly clean to stop any water seepage. Your best bet is to replace the flapper with a new, very pliable one, then make sure your adjustment is correct and you have slack in the chain. A picture of the inside of your tank would really help us to help you.

 

[jtorm]

I agree I would definitely replace the flapper first and try that. If that doesn't work it could also be the flush valve isn't tight enough to the tank and it is leaking through that seal (but not as likely)

 

[DFBonnett]

Replace the flapper and clean the area inside the tank where it seats. Flappers age and lose elasticity. They can look fine but just leak a tiny bit, exhibiting the symptoms you describe.

 

[LiLi]

Thank you for all the replies! I (very nervously) replaced the flapper, but the problem hasn't resolved; the toilet is still refilling after a slow leak. I need to fix the fill valve?

My camera is old, but I will try and figure out how to post a picture!

 

[LiLi]

Here is a photo. Hopefully it helps!

 

[havasu]

First of all, is the black hose (leading into the center tube) touching the water? If so, you may be siphoning out water unknowingly. Also, the chain to your handle seems very tight. If you remove the chain, does the water still escape under the flapper? Lastly, I dislike your ball float fill valve since they seem to always be problematic. I would recommend replacing with a Fluidmaster 400 A, which is about $10, and can be picked up at any big box store.

 

[Mr_David]

Even a new flapper can leak. Sometimes because they are slightly warped.
The most common callback. I have gone through 3 or 4 flappers sometimes on one service call. Dye testing the tank water will reveal tank leak into bowl quicker than waiting to see if tank drops a 1/2"

The ballcock type fill valve like you have does not normally siphon out into over flow when the refill tube is stuck down inside the overflow to far. The Fluidmaster fill valves will siphon water out of tank, but they are far superior to a ballcock fill valve.
You just have to install the refill with the air gap clip to prevent the siphon.

 

[gendow]

The overflow tube mounts to the tank (not the bowl) via a thick spongy gasket locked on by a large nut that sits between the tank and the bowl which another thick spongy gasket. It could be this thick spongy gasket that is leaking into the bowl thus dropping the float level which in turn is refilling your tank.