ghost flushes and misplaced fill tubes

[Doug Lassiter]

So my toilet was starting to do "ghost flushing" which is where the tank fills very briefly, when the toilet hasn't been flushed. Just for a few seconds. Very clearly, one reason for this could be a bad flapper valve, such that water was leaking out of the tank. My flapper looked good, but I replaced it anyway. Didn't help. But then I heard that a SECOND reason for ghost flushes is where the end of the fill tube is submerged. That's the tube where the water comes out of the float valve. Mine was indeed submerged, and I pulled it up. Boom! Ghost flushes gone. That's excellent, but I'm left puzzled. How does such a misplaced fill tube cause a ghost flush? Doesn't seem to make any sense. Is the float valve getting confused in some way? Explanation, please.

Addendum: OK, I see it posted elsewhere that if the end of the fill tube is in the tank water, the float valve can actually suck a bit of tank water back, making the tank level *slightly* lower, such that the float valve opens up very briefly. But WHY does the float value ever want to suck water backwards???

 

[Geofd]

I would have to research that but my guess would be a loss of pressure because something else is being used,and the water goes toward that fixture but that's just a guess

 

[Doug Lassiter]

Yes, that's my guess too, but I just have no understanding why a valve and pipe that shoots water one way would, all by itself, choose to suck up water in the other direction. That is, what is producing suction in that fill valve???

It's interesting that this fix is called out in precisely one website. Most plumbing websites just say, eh, you got ghost flushes? Change out the flapper! (Or, more painfully, change out the flapper seat.) If that doesn't work, GET A PLUMBER!

Now, before this started, I had been doing some screwing around with the fill pipe, anchoring it better, so the fact that it was submerged was my fault.

 

[havasu]

The tube too low in the flush tube creates a siphon effect, and will suck water from your tank back into your bowl. This triggers the fill valve, and how you create ghost flushes.

 

[Doug Lassiter]

OK, that's pretty clear that's what's happening. But it begs the question, WHY is there a siphon effect? What is sucking on the fill tube? The fill tube is connected to a water walve that turns on and off. When it is on, the water pressure in the main pushes water through the fill tube. When it is off, nothing should be happening in that tube. Sucking water into the bowl? That makes zero sense. The fill tube and water valve aren't connected to the bowl. The only connection the bowl is the seat under the flapper which has nothing to do with the fill tube.

 

[havasu]

It is like two barrels of water connected to a parallel hose. The water will seek its own level. If the hose is lower in the fill tube, it will draw water from the tank until it equals the level of the hose. This begins to activate the fill valve, and the ghost flush.

 

[Doug Lassiter]

The fill tube, that shoots water into the tank, is pretty horizontal, except at the end, where it dips into the overflow pipe. So the upper part of the tube, at the valve, is supposed to be sucking on the lower part of the tube, in the tank? Nope. Siphons don't work that way. A lower barrel doesn't siphon into an upper barrel.