How To Repair a Cast-Iron Toilet Flange

If your toilet is leaking, you may want to check your toilet flange. Cast-iron toilet flanges were commonly used in older homes due to their durability and strength. However, these flanges can corrode or break over time, leading to leaks and unstable toilets. In the video above, This Old House plumbing and heating expert Richard Trethewey shows a homeowner how to tackle this task and provides valuable insights.

Signs Your Cast-Iron Toilet Flange Needs Replacement

Some of the most common causes of cast-iron flange damage are age-related deterioration, moisture corrosion, improper installation, and shifting house foundations. There are several red flags that indicate a failing cast-iron toilet flange: 

• A loose or rocking toilet
• Foul odors emanating from the toilet area
• Visible rust or corrosion on the flange
• Water leaking around the base of the toilet

Preparing for the Repair

Here are the tools and materials you’ll need to repair your leaky toilet:

• Close-quarters hacksaw
• Closet bolts
• Cold chisel
• Hammer
• Hex bit sockets
• Pliers
• Replacement flange (appropriate for your specific situation)
• Ratchet wrench
• Screwdriver
• Stiff blade putty knife
• Wrench
• Wet/dry vacuum
• Wax ring or flexible gasket

Removing the Toilet

The first step in repairing a cast-iron toilet flange is to remove the toilet itself. Wear protective gloves and eyewear and ensure proper ventilation in the work area. Use caution when handling sharp tools and broken flange pieces.

In the video, Trethewey demonstrates the proper technique for toilet removal. Here are the steps he takes:

1. Close the shut-off valve behind the toilet to stop the water flow.
2. Flush the toilet and hold the lever down to drain water from the tank and bowl.
3. Use a large sponge to remove any remaining water from the tank and bowl.
4. Disconnect the water supply line from the tank.
5. Remove the nuts from the closet bolts on each side of the toilet base. If the nuts are rusted in place, cut through the bolts with a close-quarter hacksaw.
6. Rock the toilet back and forth gently to break the wax seal, then lift and remove the toilet from the bathroom.

Inspecting and Removing the Old Flange

Once the toilet is removed, you can assess the condition of the cast-iron flange. Use a stiff-blade putty knife to scrape away the old wax ring or gasket. Unscrew and remove any extension rings to expose the cast-iron closet flange.

As Trethewey discovers in the video, the flange may be severely corroded or even completely disintegrated. Examine the flange for visible cracks, rust, or missing pieces. Check if it’s sitting flush with the floor or if it’s recessed due to additional flooring layers. Inspect the surrounding floor for any water damage or rot.

If the flange is severely corroded, use a hammer and cold chisel to carefully break away the remaining pieces. Pull the loosened flange out of the cast-iron drainpipe with a pair of pliers. Clean the area thoroughly, removing all debris and rust from the drainpipe and surrounding floor.

Installing a New Flange

Measure the inside diameter of the existing drainpipe. Consider using an expandable flange for pipes that don’t fit standard sizes. Make sure the new flange will sit at the right height relative to the finished floor.

Follow these steps to install the new flange:

1. Set four wood blocks around the drainpipe to hold the new closet flange at the correct height.
2. Install a plastic expansion closet flange into the cast-iron drainpipe.
3. Use a ratcheting hex-key wrench to tighten the four screws on the inside of the flange until the flange is tightly wedged into the drainpipe.
4. Slide two new closet bolts into the slotted keyways in the flange.

Reinstalling the Toilet

With the new flange in place, it’s time to reinstall the toilet. Take the following steps:

1. Place a new wax ring or flexible gasket on the flange.
2. Lower the toilet onto the flange, aligning it with the closet bolts.
3. Press it down to compress the wax ring or gasket and create a watertight seal.
4. Install washers and nuts on the closet bolts, tightening them alternately to ensure even pressure.
5. Trim any excess bolt length and install decorative caps.
6. Reconnect the water supply line and turn on the water.
7. Flush the toilet multiple times to check for leaks and proper operation.

Troubleshooting Common Toilet Issues

Even with careful installation, you may encounter some issues that need addressing. Here are some common problems and their solutions:

• Leaks around the base: Check that the wax ring is seated and the toilet is level.
• Rocking toilet: Use shims to level the toilet, then caulk around the base to prevent water infiltration.
• Weak flush: Check that the tank’s water level is set correctly and the flush mechanism is functioning properly.

Maintaining Your Repaired Toilet Flange

To prevent future issues with your toilet flange, regularly inspect the area around the toilet base for signs of leaks or movement. Address any toilet clogs promptly to prevent excessive pressure on the flange and seal. When cleaning, avoid harsh chemical cleaners that can corrode the flange or pipes. Replace the wax ring or flexible gasket every few years to maintain a good seal.