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How To Replace A Toilet Flange

If you need to repair a toilet flange, the job isn't always easy and may require assistance from a licensed plumber. There are a couple of possibilities with replacing a toilet flange yourself, and everything depends on the size and type of pipe.

Follow these steps to replace a toilet flange:

If the pipe has a 4-inch inside diameter:

  1. Buy an inside closet flange. This toilet flange is designed to glue on the inside of the pipe or expand inside the pipe.
  2. Leave the old toilet flange right in place and glue on the new one at the right elevation for the floor, if it's plastic.
  3. The flange should be sitting with the bottom edge flush with the top of the floor. If it isn't, then you will have to cut away the old flange.
  4. If the plastic pipe has a 3-inch inside diameter, you’ll have to remove the old flange from the outside of the pipe. This is a difficult task because you have to make the opening around the flange large enough to peal the old flange off the pipe. In addition, there is no guarantee of success with this type of toilet repair; it takes a plumber many years to master the art of splitting the glue joint without damaging the pipe.
  5. If a closet flange is cast iron, then you would have to use a hammer and chisel to break the flange and remove it.

If it is a 4-inch pipe:

  1. Use an insert closet flange that has a rubber gasket that expands on the inside to seal against the inside pipe surface.
  2. Remove all the old build-up in order for the toilet flange to seal properly.
  3. This can be done by scraping or sanding with a wire brush on a drill. Use a little silicone on the gasket when you begin tightening it up.

If it is a 3-inch cast iron pipe:

  1. Break off the old toilet flange from the outside.
  2. Install a toilet flange on the outside. This can be done with a hammer and chisel. If the flange is cast iron with a rubber gasket, you should be able to remove the cast iron with a hammer and chisel, remove the rubber gasket with a sharp knife, then replace the gasket and the flange.
  3. If the closet flange is lead and installed on the outside of the pipe, you will have to remove the old flange and re-caulk it, and then pour a new lead joint. You can also install an expanding one on the outside, but that would require breaking up the floor to get the flange down into the floor.
  4. After setting every flange, make sure you screw it to the floor so it will not rise up when you tighten down the toilet. Bolt the flange down through the holes supplied in the flange with concrete or wood anchors that are galvanized or brass so they won't rust and break.

Additional tips for a 3-inch cast iron pipe:

  • When you tighten the toilet flange, never use more than a 6-inch crescent and two fingers on the handle to get the nuts tight.
  • In addition, if you use a plastic flange, make sure you use one with a stainless steel outer ring, so it won't rust and is stronger than the plastic itself. Again, no toilet should be tightened so tight it breaks the flange.
  • A toilet should always be set level and the edge that touches the floor should be sealed with calk to prevent it from smelling.

For more information about toilet flanges or other bathroom plumbing issues, Visit our Plumbing Videos library and our Bathroom Plumbing blog.