: I have a two story house with basement on sewer. Upstairs master toilet bowl drains, tank stays full. 2nd upstairs toilet is fine. 1st floor toilet is fine. The draining started about 2 or 3 weeks ago. No leaks visible and flushes fine. I do notice that when flushing you get a burst of bubbles out of the trap area. Shower and sink and tub are on the same stack and seem to drain fine. Also do not notice any siphoning when other items are draining. Any ideas? Other postings indicate a possible china crack that lets water down the drain and not the floor or 1st floor ceiling.
The most common reason for this is that the vent is plugged. The toilet will usually be vented from the sink. (wet vented) If the vent is plgged this with cause the problem. Have a drain cleaner snake all the vents in the house to see if the problem goes away.