Our toilet will often go into a mood and start hissing. This will go on until I manually operate the filling mechanism to fill the tank higher.

I suspect that it is somehow not filling enough and then slowly leaking until a point where it just triggers the filling mechanism to create the hiss. However, there is no leak into the bowl, and I do not know why the top of the post (as seen in the video) is spurting water.

Video: Hiss is about 4-seconds in.

Any ideas?


The flapper might move a little to the side when flushing, so you fix it it manually. Have the same thing with my TOTO 1.4 gpf. Changed the flapper several months ago, the hissing stopped for a while, now started again. I washed the flapper with lemon juice and soap to remove any calcium carbonate that might accumulate - it reduced the frequency of the hissing but didn't solve it completely. I guess it is the flapper/flush opening contact that got lousy. Maybe a thin gasket would do the trick. Tell you when I check.

Good luck!

  • So - to update almost a year later... Looks like there is a slight leak into the bowl (tested with food colouring), but the hissing stopped a couple months after my initial post and doesn't seem to have returned. A local plumber suggested that it might have been something to do with air bubbles in the vacuum-tube (? -- far left in the video) slowly clearing over time, now finally cleared. I should have thanked you a year ago for your quick reply - my apologies for having not done so. Thank you! I will let you know if anything else comes up. Thanks again! irfaan – irfaan Feb 23 '16 at 1:36

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