So my mystery toilet problem update:
After two days of not working, the toilet spontaneously started working again. This is always the pattern. I think it is somehow related to the weather. I suspect that it is caused by the winds blowing from the northeast. I am going to keep track of it. Why do I think that?
Well, I do believe that all of those who commented on my previous post are correct in that it is a vent problem. Let me explain:
I live in a 4 bedroom, 2 bath house. The roof is a gabled roof, with the roof ridge running east to west across the house. This is important to my hypothesis.
There are two lines for sewage that are under my house. They both run north-south. One line is on the east side of the house and services the kitchen and laundry room. It has two vents: one vent pipe that runs up the wall and emerges from the northern slope of the roof, and the second is an under sink AAV valve that is in the island that my kitchen sink is mounted upon.
The second sewage line runs down the west side of the house from the master bath’s commode (which is on the southwest corner of the house), past the his and hers sinks, under the shower, and on through the guest bathroom. There is a vent that extends up the wall and emerges from the roof above the guest bathroom, again on the northern slope of the roof. The only other vent for this western line are two AAV valves located under the master bathroom’s sinks.
Both vents are clear. The sewage lines are clear. I know, it cost me a $500 plumbers visit, after which they told me nothing was wrong with the plumbing.
My hypothesis is this:
The vents are both on the northern slope of the roof. When the wind is blowing from a certain direction (probably a northern one), the wind is pressurizing the pipes through those northern vents. Once the sewage line is pressurized, this pressure prevents the toilet from flushing. The only thing that could destroy this hypothesis is the fact that no other fixtures, including the toilet in the guest bathroom, which is still on the other line, continues to work.
I don’t think it is malfunctioning AAV valves, because while the toilet was malfunctioning I removed the valves under the master bathroom sinks, and the toilet remained dysfunctional.
I am frustrated, the wife is getting aggravated, the plumbers are clueless (yet still billing me for visits), and I am out of ideas.