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?

2 Answers 2


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
    Commented Feb 23, 2016 at 1:36
  • @irfaan The proper way to say "thank you" at Home Improvement is to up vote the answer and click the check mark next to it.
    – FreeMan
    Commented May 29, 2020 at 12:36
  • Since OP never came back, here's a thank you +1
    – FreeMan
    Commented Sep 29, 2021 at 14:17

The issue is more likely to do with the linkage for the actuator, than the actual flush valve or full valve. Make sure the plastic pins that contact the flush actuator buttons are not too long. They can be “off” or slightly too long by a very small amount, Causing the issue. Also, make sure the actuator is installed so it fits flush to the wall, all the way around. If it won’t sit flush, it could be because the flush linkage is a bit long, causing the issue.
There is also a diaphragm located at the top of the fill valve. It’s an easy and inexpensive replacement part. If you’re already in the carrier, you may as well change it. The flush valves usually aren’t an issue with these.
The top of the fill valves are designed to leak into a small tray to act as a counterweight for the fill valve to stop gradually.

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