Toilet Flange Basics
A toilet flange has two parts. The first is a short length of pipe that fits inside the waste pipe and is permanently attached -- usually by gluing. The second part is a ring that gets screwed to the subfloor. The ring has tracks that hold the toilet bolts that keep the toilet mounted tightly to the floor, and it's the ring that most often needs repair. Some flanges have cast-iron rings that corrode in the moist atmosphere under the toilet, while others have plastic rings that may not corrode, but can break. Improper installation can also make a flange fail. You can usually fix broken and improperly installed flanges without the need for replacement.
Consequences of Flange Problems
When a flange ring begins to deteriorate, it's no longer able to hold the toilet securely, and the toilet may rock whenever someone uses it. When it does, it can open a gap in the wax ring seal, and water can spill during a flush. This water is a serious problem -- even if there isn't enough to see on the floor, it may be soaking and rotting the subfloor and joists, which makes the rocking progressively worse. This can happen even with a new flange, if the top of the flange has been installed above level of the finished floor or more than 1/4 inch below it.
Repairing a Broken Ring
To make any flange repair, you first need to remove the toilet and clean up the old wax ring. If part of the ring has broken or corroded, repair it with a full or partial repair ring. This circular or semi-circular piece of metal fits over the existing flange ring and gets screwed to the floor through the holes in the existing ring or through holes that extend over the ring. If you discover the cause of a leaking flange is the fact that it has been installed too far below the finished floor, you can raise it with a flange extender -- a plastic repair ring that sits on top of the existing ring to raise it.
Replacing the Ring or the Flange
If you discover that the flange ring is too corroded to save, it's possible to remove the old ring by cutting it with a reciprocating saw or similar tool, and digging it out from around the waste opening. You can then install a new ring by fitting it around the opening and screwing it to the floor. In some cases, removal of the entire flange may be necessary; this is a job that usually requires a plumber, because you have to cut out part of the waste line and replace it. In some cases, you can fit a replacement flange into the waste pipe without removing the existing flange -- it has a rubber compression fitting that makes a watertight seal.