Strange happenings

Why would the toilet fill with water when the tub / shower handle is turned off? This happened on my inspection today and has left me baffled.

Well, in my house the toilet is independent from the tub.

Your question has me baffled…

Do you mean that the tank filled (or filled faster) , or the water level in the bowl rose?

When the water to the tub was shut off, water ran into the toilet bowl (the handle was not flushed)- it did not actually fill the bowl

What happened when the tub was turned on??

The garage door went up…

Waddahey…that happens at my house, too. Isn’t supposed to do that??

Kidding aside…it sounds like a possible cross-connection. Check out this really good website:

Nothing happened until the tub was turned off.

If this was a pressure assisted toilet, I seem to remember a service bulletin some years back about a check valve that can fail that will cause this problem when other fixtures are cycled. I don’t remember the brand that the service bulletin was about.

Interesting information Marc. I never knew that. However this was not a pressure assisted toilet.

Also, the master bathroom toilet would not flush for me or the client. When the agent went in, it flushed. Go figure. Something definetly not right with the plumbing system here.

I guess the owner will have to call the agent each time…heh, heh, heh…

Could be a bad ball ****.

Please excuse all the improper terms and my attempt to explain what I think is happening…I have seen this before and have some knowledge of pressure and flow due to my other life.

When the water is sitting still (all fixtures off) it is at a certain pressure…I call it static pressure and I’m sure others do as well :wink: Static pressure is almost always higher than the next kind of pressure. (it may well be that static is ALWAYS higher…I don’t know and I don’t care)

When the tub is running the “operating” pressure goes down to a level that is less than the “static” pressure with all fixtures off.

When you shut the valve off…to the filling tub…you get a spike, sometimes a very large spike in the pressure…as the water “stops” moving so to speak.

This spike could be causing the fill valve to come on momentarily as its mechanism fights the pressure and cannot hold the water back…maybe it is beginning to go bad.

You didn’t tell us what kind of fill valve it was…you also didn’t tell us if the toiled ran awhile when this happened or did it just kick on and run…

Perhaps the flapper is going bad and it is a coincidence as well.

Also, there could be a cross connection…but is it possible for the tub running to cause enough suction to siphon the water from the tank into the plumbing?

There are more questions than answers with this one…I would love to witness it.

While the tub is running…the pressure


I think you are very close. Another inspector freind came up with this.

“If the water level control valve fails to firmly and securely seat and shut off, the pressure created by turning off a high volume use valve quickly creates a large pressure build-up (which is the cause of most water hammer, and why there are anti-water hammer arresters on supply lines which have automatic closing vales). That increase in pressure is trying to force water back out the other way (from which it came) and the toilet is right there, and the valve is likely not fully seating closed, so it gets pushed open, filling the tank, which then fills the bowl, and, when the bowl is filled far enough fast enough, it will siphon out (flush).”

When I was a service plumber that would be the first thing I would check. You would be surprised at what problems a simple ball **** can cause.

It’s a ball C-O-C-K. I’m not being nasty here but evendently the program thinks I am.

Are you wanting to know what the cause is so you can write that in the report? If so, that goes beyond the scope of the home inspection and gets into troubleshooting. It “could” be any number of things. Unless we know exactly what is causing the problem or the anomaly we should refer it to the experts. Even then it is extremely thin ice to diagnose problems as we might not be right, the buyer fixes what they now believe to be the cause and later it turns out not to be the cause.

The definition of cross-connections is the actual or potential connections between potable and non-potable water supply; constitutes a serious public health hazard. There are literally dozens of different ways for cross connections to occur. Anytime you have supply water moving from one fixture to another it is safe to bet it isn’t normal and needs to be addressed and corrected. As explained by Tony, one of them is unequal pressures between units or within a system.


Not diagnosing here. I already wrote it up for repair by a licensed plumber. I was just curious if anyone knew what might cause the problem, and how serious it might be.

Thanks for your reply. Not trying to overreach anyone but I see so many HI get over into problem analysis and end up having a problem. Glad to hear your response. I find even for myself having to pull back and resist the urge to develop a diagnosis and a “solution” for my customers. I think this business attracts people who genuinely like to help and are naturally curious, detail oriented and opinionated.