[Doublej]

I was getting phantom flushing where the toilet would run for a few seconds and then stop. So I replaced the fill valve and the flapper.

That didn't fix the problem but once during an episode caused by flushing the toilet then turning on the sink to wash my hands I noticed the problem appears to be that something is causing the flapper to raise slightly for a short period of time.

I am not sure what to do at this point. How does turning on the water in the sink cause a toilet flapper to rise? Is there normally a vacuum in the flapper valve tube that causes the flapper to stay closed that is being temporarily disrupted in my case?

Should I just try a different type of flapper?

[Wayner]

Sounds like a venting issue to me. Without proper sewer pipe venting, all kinds of weird things can happen. Air needs to come into the system to allow the water to drain away. Without it, the system will "burp" its way to drainage. Your toilet may be burping thru the flapper valve to get air.........

'ner

[Peter J]

Wayner probably has it nailed.

Modern toilets will have, assuming no hacked remodels, a vent within 5' of the toilet. Birds nests, squirrels and all manner of weirdness can partially or completely block a vent.

Imagine a big slug of water being introduced into a 3" pipe. It has to have a similar sized slug of air following it or it doesn't go or is slowed down considerably. Same principle as holding your finger over end of a straw and lifting it from the liquid it's standing in.

Any plumbing mods recently? Any other plumbing related events recently?

Venting is done differently sometimes terminating into a central stack and sometimes separate vents for toilets in particular. Tell us more about location of bathroom in the house and I can better direct you to identifying vent if you're going to DIY. This is usually not a hard fix.

I doubt there's anything wrong with the toilet...they're actually pretty simple devices.

[JerryM]

Sounds like a venting issue to me. Without proper sewer pipe venting, all kinds of weird things can happen. Air needs to come into the system to allow the water to drain away. Without it, the system will "burp" its way to drainage. Your toilet may be burping thru the flapper valve to get air.........

'ner

Not to *get* air, but to *release* air, yes?

The flapper, in your example, has become the vent, thus burping (releasing) air. A flapper trying to *get* air would suction to a more-closed position, no?

[Doublej]

House is a circa 1900 +/- three story single family converted to three apartments and then two condos. I occupy floors 2 and 3. Problem toilet is on the second floor. Kohler 2 piece 1.6 gallons per flush toilet.

No plumbing changes of recent. The toilet and kitchen sink for the first floor are on the right side middleof the house. My kitchen is on the right side middle but the two toilets are on the left side. Vent pipe that sticks out the roof is on the left side of the house.

At some point a washer dryer hookup was added to the third floor adjacent to the bathroom.

[FullRangeMan]

Seems over pressure water in the pipe.

[Peter J]

House is a circa 1900 +/- three story single family converted to three apartments and then two condos. I occupy floors 2 and 3. Problem toilet is on the second floor. Kohler 2 piece 1.6 gallons per flush toilet.

No plumbing changes of recent. The toilet and kitchen sink for the first floor are on the right side middleof the house. My kitchen is on the right side middle but the two toilets are on the left side. Vent pipe that sticks out the roof is on the left side of the house.

At some point a washer dryer hookup was added to the third floor adjacent to the bathroom.

Assuming you can get on the roof, a sewer snake can be run down the vent. One can also try to pressurize the blockage by running a hose in the vent and hoping shear weight of the column of water forces the clog out. The risk is that it drives whatever's causing the blockage in further/tighter.  The closest one to bathroom is where I'd start.

  Older construction that been modified can get weird, but I'm assuming the problem has just appeared so that backs up the presumption of a clogged vent. By and large drain systems don't just up and fail, but with old galvanized and cast iron pipe it's a possibility.

I should add that it may be you can actually see the clog if it's a bird or rodent nest (or tennis ball or potato or meteorite). Shining a flashlight down the vent might tell you all you need to know.

[Peter J]

Not to *get* air, but to *release* air, yes?

The flapper, in your example, has become the vent, thus burping (releasing) air. A flapper trying to *get* air would suction to a more-closed position, no?

Technically yes, but the air will want to come form wherever the path of least resistance is and can manifest in some odd ways.

[Peter J]

Seems over pressure water in the pipe.

Drains in above grade situations are completely functional via gravity. There is no "pressure" present in drain systems as there is in supply lines.

[FullRangeMan]

Drains in above grade situations are completely functional via gravity. There is no "pressure" present in drain systems as there is in supply lines.

I live in a building that seems to be the case, seems the OP live in a house.

[Peter J]

I live in a building that seems to be the case, seems the OP live in a house.

I suppose I should clarify. I'm talking about residential plumbing in the US...such as a house.

[FullRangeMan]

I suppose I should clarify. I'm talking about residential plumbing in the US...such as a house.

OK, when my hydra valve locked in open position the problem was the seal and spring that were worn.
It was one similar to this:

[Wayner]

Technically yes, but the air will want to come form wherever the path of least resistance is and can manifest in some odd ways.

Peter is hitting the proverbial nail on the head here. Since the house is really old, the vent stack pipes are probably rusted to hell and have little to no affect. Perhaps a snake will clear out the derbies, but I suspect some re-piping will be required to fix the problem. Time to call a real good plumber......

[Doublej]

Thanks. Not what I wanted to hear but what I needed to know. Can I live with it as is for a while or is this something that needs to be addressed pronto?

[Peter J]

Thanks. Not what I wanted to hear but what I needed to know. Can I live with it as is for a while or is this something that needs to be addressed pronto?

It may not be as bad as you think...can you get on the roof and have a look down the vent? That'd be my first move. Leaving it for a while probably isn't a big deal, but when vents get plugged the air wants to come from somewhere which means it can suck the water out of drain traps and you'll get some sewer-y smell.

Squirrels (young & stupid) sometimes head down vents in search of more stupid and can't get back out. What  a way to go, huh? Birds and rats too.

Did it happen rapidly or progressively worsen?

[Doublej]

It's been around for a while. It seems to be no more frequent than it has been in the past. I won't go on the roof as it is three stories with a Dutch colonial style roof meaning too steep for me.