New toilet running for a few second, but only about 10-15 minutes after shower is over.

[ShelzMike]

This one has me stumped as stumped can be. I recently completed remodel of our single (only) bathroom as well as a complete tear out and re-plumbing of the whole house DWV system, including abandoning the septic and running new sewer line for a new sewer connection. When I say all of it, I mean all of it.

House has bath/shower, toilet, lav, kitchen sink, utility sink & washing machine (both of these in the basement). All is up to code and every fixture has it's own vent, and re-venting exists where necessary.

Here is what is driving me crazy. Since we have been on lockdown, we haven't been taking a shower every day (most days) because there is no real reason to and it allows us to save some water. I mention this because what I am going to describe ONLY happens at a very specific point in time.

For whatever reason, anywhere between 10-15 minutes after someone finishes taking a shower the brand new toilet will run for about 5-7 seconds and then stop, just as it would if it was actually flushed.

Toilet is not leaking at wax, nor at bowl/tank connection. This is an American Standard, btw. Not sure of the model number, but it isn't the most expensive, but also isn't the cheapest either.

I shut off the valve and put food coloring in the tank and let it sit for 2 hours during a non shower period, and nothing. Water level is the same, no dye in the toilet bowl. (I plan on doing this same test just before someone takes a shower next time to test that situation).

Note, this running does not happen ever when no one is taking a shower, but every time someone does, without fail it will run as I mentioned above no sooner than 10 minutes after the shower is over and no longer than 15 minutes.

Any suggestions because I am almost at the "oh well, what can you do" point and will just learn to ignore it

 

[Reach4]

Pretty wild. Here is what I suspect:

After a hot shower, the water in the WH expands. In the old days, the water would just expand out into the city mains, but now cities are putting check valves in place.

Your fill valve is somehow reacting when the water pressure is high. Now is it just serving as a straight pressure release, or did the pressure just serve as a trigger to something on the razor edge. How high is your water with respect to the overflow? Does the refill tube go down the overflow tube, rather than being positioned above? You could take a look. But anyway, I think the water pressure controls the timing of the even.

You should have a thermal expansion tank. If you have one, its precharge may not be right, or it could have failed. The air precharge ideally would be the same as the max the city sends you normally. That tank is normally empty of water, unless it is absorbing thermal expansion.

There use to be a fill valve that would release pressure at maybe 100 to 120 or so by design. It was a fill valve and pressure release valve combined. It was an alternative to a thermal expansion tank for areas without a water shortage. I don't think it is offered any more.

 

[Sponsor]

 

[Dj2]

I would look at the flapper more closely.
Do the dye test again, but check the tank water level after a longer period of time than 2 hrs.

 

[Jeff H Young]

if the tank level drops you got an issue with flapper or some how tank leaks to bowl. So you 100 percent eliminated that possibility.
Normal water pressure. Eliminate any issue there. Like it goes from 30 psi to 100 psi.
So all things normal leaves one item to be culprit. bad , damaged, defective fill valve. Clean and flush or replace but ineither case flush it out. Easy as Pie!

 

[ShelzMike]

Pretty wild. Here is what I suspect:

After a hot shower, the water in the WH expands. In the old days, the water would just expand out into the city mains, but now cities are putting check valves in place.

Your fill valve is somehow reacting when the water pressure is high. Now is it just serving as a straight pressure release, or did the pressure just serve as a trigger to something on the razor edge. How high is your water with respect to the overflow? Does the refill tube go down the overflow tube, rather than being positioned above? You could take a look. But anyway, I think the water pressure controls the timing of the even.

You should have a thermal expansion tank. If you have one, its precharge may not be right, or it could have failed. The air precharge ideally would be the same as the max the city sends you normally. That tank is normally empty of water, unless it is absorbing thermal expansion.

There use to be a fill valve that would release pressure at maybe 100 to 120 or so by design. It was a fill valve and pressure release valve combined. It was an alternative to a thermal expansion tank for areas without a water shortage. I don't think it is offered any more.

This..is honestly a very astute hypothesis and one that I think may very well actually be correct. From what I am understanding what you are saying is that essentially the toilet could almost be acting like an expansion tank for the HW heater back pressure. Do you know the one thing I have yet to replace (but will be in the next couple of weeks)? Yep, the HW heater. Do you know why? Right again, pressure build-up. I have changed the pressure relief valve on the current (quite old) one and I have to keep a bucket under the discharge pipe because it still leaks. Not a ton, but daily. Do you know what my hot water heater lacks? Expansion tank! I would have never thought this to be the issue. Wouldn't have crossed my mind. So you very well may could have solved the mystery of why it ONLY does it after a shower.

The other suggestions of the flapper are usually the most logical; however, considering the toilet is brand new and considering the fact it literally never has this issue at any other time and does have the issue after every single shower, and only one time each time, lends itself to your theory being correct.

We can live with it for a few weeks until I get the HW heater swapped out, but I will be sure to come back and update if this indeed solved the problem (Will be adding expansion tank as well).

 

[Jadnashua]

WHere I live, it is code to have an expansion tank in the system. From a practical viewpoint, it is not 'necessary' unless the system is closed (i.e., there's something in it to prevent that expanding water to flow back into the supply system). From your description, the T&P valve opening is normal. They are not designed to be activated regularly, so if the WH wasn't going to be replaced, you would want to replace it to ensure it could still seal and work when it needed in a fault condition. The feds have been pushing all public water systems to install check valves to prevent any possibility of contaminants from a home being pushed back into their public water systems...it's just a matter of time when all of the utilities complete that task, if it's not already been done to yours. Note, a PRV creates a closed system, so you may have done that to yourself even if the utility did not...

It doesn't usually take all that much of a leak to keep the pressure below 150-psi when the T&P should open, and a toilet valve is often one of the weakest links, and will let water out to relieve the pressure.

 

[wwhitney]

If there's HW expansion going on, you can relieve the pressure by leaving a faucet open to a very slow drip (maybe one drop every few seconds). Then if the toilet running reliably occurs with 15 minutes after every shower, you can try that at the next shower and see if it keeps the toilet from running.
If so, that would give you confidence that adding the expansion tank would fix your toilet running behavior.

Cheers, Wayne

 

[Jeff H Young]

If there's HW expansion going on, you can relieve the pressure by leaving a faucet open to a very slow drip (maybe one drop every few seconds). Then if the toilet running reliably occurs with 15 minutes after every shower, you can try that at the next shower and see if it keeps the toilet from running.

Never hurts to put a gage on it, It wont lie, I think itsalmost a sure thing increased pressure is part of cause but are all the toilets doing it? I think the fill valve is a bit week but cant know . rather than run the faucet . why not check pressure? Didnt see him say system is closed? When doing a full remodel on a house debris gets in places like the fill valve. even on a new toilet. Expansion tanks are a good thing but Id at least clean it out (fill valve)

 

[wwhitney]

are all the toilets doing it?

Per the OP, it's a one toilet house.

rather than run the faucet . why not check pressure?

Because the faucet test works well enough, and doesn't require a pressure gauge, in case the OP doesn't have one?

Cheers, Wayne

 

[WorthFlorida]

Definitely, the water pressure is pushing the flush valve to open. Old temperature pressure relief valves on water heaters do occasionally fail by leaking. A good one is suppose to open at 150 PSI. If your pressure does get that high often you'll be having a lot of other issues.

 

[Jeff H Young]

Definitely, the water pressure is pushing the flush valve to open. Old temperature pressure relief valves on water heaters do occasionally fail by leaking. A good one is suppose to open at 150 PSI. If your pressure does get that high often you'll be having a lot of other issues.

He changed the t and p because it was expelling water the new one does the same thing. I missed that too , He obviously has high pressure and or possibly a closed system. Unknown pressure . He is just going to change out water heater and install expansion tank, hope that takes care of it

 

[ShelzMike]

Well, gentlemen, we don't have a definitive conclusion, but testing has proven fruitful thus far. Last night, I opened up the lav to a drip for pressure relief and showers ensued. Not one single time did the toilet run after the shower like it had been every time. This does lend itself to the pressure issue. No other elements or conditions were different last night than any other night.

To clarify a few things also - yes, we have only 1 bathroom. We actually do have 2 toilets (temporarily) as there is a "Pittsburg Toilet" in the basement that we had to use during the remodel that is still connected. However, it is the lowest point in the house both drain and supply which may make some difference. Not sure.

I do not have a check valve in my system that I installed. Expansion tanks are not required here; however, the town recently just replaced all of our meters. I know that part of the reason was to add remote reading and connectivity, but I sort of remember seeing it mentioned they also included a backflow preventer check valve, but could be wrong about that.

I am not just simply going to replace my HW heater to solve this problem, that would be really throwing it at the wall to see what sticks. Rather, I had already been planning on changing it anyhow as it needs to be replaced. Current one is from 1992 and worked well up until about a year ago when I started noticing the T&P expelling (even a replacement expelled, but less so). Even though an expansion tank is not required here, I am going to put one in while I am at it as it won't hurt and they aren't expensive so might as well.

 

[Jeff H Young]

A pressure reducing valve might be needed too. but if expansion tank solves issue and your happy that pressure is not excessive your good! I recomend testing pressure gauge about 8 bucks online. thats just what I do but very high pressure and these issues are very common in my area . We get many symptoms here running toilets, faucets and showers that drip , Ive gotten burned myself replacing cartridge and still drips check pressure and its over a 100. anyway none of this is new to me but I do sometimes overlook the obvious. Recently I was getting fooled by a bad gauge ( the cheap ones arent always that good) It was old but not trusty. I bought a pair But I use at least weekly

 

[wwhitney]

I agree on checking the static pressure with a gauge to see if a pressure reducing valve is also needed, in addition to the expansion tank. If the baseline pressure is high, then it doesn't take as much thermal expansion to reach excessive pressure. Definitely worth checking.

But the original behavior is almost certainly thermal expansion at this point. The OP could triple check by verifying that the toilet runs after any extended hot water draw, and doesn't run after cold water shower draws. So run the shower cold only for 5 minutes, should be no toilet running. Run the kitchen sink hot only for 5-10 minutes, the toilet should run just like after a shower.

Cheers, Wayne

 

[Reach4]

I do not have a check valve in my system that I installed. Expansion tanks are not required here; however, the town recently just replaced all of our meters. I know that part of the reason was to add remote reading and connectivity, but I sort of remember seeing it mentioned they also included a backflow preventer check valve, but could be wrong about that.

Backflow preventer valve is a check valve. Your symptoms prove the need for a thermal expansion tank. There are various sizing guides and calculators. The smallest may be enough. If you get the next size up, and you did not need that, it does not hurt, except for the increased purchase price.

A garden hose thread pressure gauge can go on an outside spigot, a laundry tap, or the drain on the water heater. You will want one to determine how much air precharge the expansion tank should get.
https://www.homedepot.com/p/Watts-3-4-in-Plastic-Water-Pressure-Test-Gauge-DP-IWTG/100175467

 

[Jeff H Young]

Backflow preventer valve is a check valve. Your symptoms prove the need for a thermal expansion tank. There are various sizing guides and calculators. The smallest may be enough. If you get the next size up, and you did not need that, it does not hurt, except for the increased purchase price.

A garden hose thread pressure gauge can go on an outside spigot, a laundry tap, or the drain on the water heater. You will want one to determine how much air precharge the expansion tank should get.
https://www.homedepot.com/p/Watts-3-4-in-Plastic-Water-Pressure-Test-Gauge-DP-IWTG/100175467

And to determine whether or not a prv is in order. good advice on pressure test This guy has spent thousands on a remodel and repipe small price for gauge take out the guess work . Expansion tank he needs for sure. Wayne and Reach 4 smart guys great suggestions!