Is the Toilet Running?
When you say that your toilet is refilling, you might mean that it is running. The water in the bowl is constantly refreshing without overflowing the bowl. Most commonly, this is caused by a problem with the mechanism that controls your flushing. The chain may have come off, the floater may be broken, or there may be some other kind of issue. Sometimes you can troubleshoot this yourself, especially if it is just that the chain has fallen off and needs to be resecured to the arm. However, more complicated fixes might require your plumber’s toolbox.
Is the Toilet Overflowing?
You might also mean that your toilet is refilling to the point that it overflows. Any overflow problem is caused by a clog in the toilet, its drain pipe, or further down the line. If any of your other fixtures are affected, that can give you a clue as to where the issue is. Your plumber can resolve overflowing toilets by removing the clog. They may use specialty equipment to break the clog down and flush it through the system. Or, they may need to scope out the pipe to discover what and where the clog is.
Either way, you can turn off the water supply for the toilet so that you stop the overflow before your plumber arrives. There should be a small valve on the line that brings water to the toilet. You can typically find this right next to the toilet. Twist the valve until the water stops and then call your plumber.
Is Your Toilet Flushing on Its Own?
The third potential issue you might be experiencing, and the least common, is the ghost flush. This is where the toilet seems to flush all of its own accord. This might be an issue caused by a motion-detecting toilet. Or it might be that the toilet has a minor leak and when the water level gets low enough, this triggers the toilet to flush. In either case, you will need your plumber to sort out the problem and potentially replace some parts.
Is the Toilet Bowl Not Filling?
You might also have the opposite problem, where the toilet bowl does not fill at all. The most likely cause of this is simply that the inlet valve is closed and is not allowing any water to pass into the toilet. Open up the valve to test this. If that doesn’t work, then you should call your plumber.