How to know your flange needs replacing
Three symptoms indicate flange failure: (1) the toilet rocks when you sit, even after retightening the bolts; (2) water seeps around the base after each flush; (3) a sewer-gas odor at floor level near the toilet. The flange is the round fitting that connects the toilet base to the waste line, holding the wax ring seal and the closet bolts. When it cracks, breaks at the slot, or rusts through (cast iron), the toilet has nothing to seal against.
Tools and parts
- Replacement flange (match your existing pipe material: PVC, ABS, or cast iron repair ring)
- New wax ring + horn (Fluidmaster #7530 or Korky Universal)
- New closet bolts and washers (5/16" x 2-1/4" brass)
- PVC primer + cement OR ABS cement (for plastic flanges)
- Hammer drill with masonry bit (for slab-on-grade)
- Hacksaw, putty knife, channel-lock pliers, adjustable wrench
- Towels and a 5-gallon bucket for residual water
Step 1: Shut off water and remove the toilet
Close the angle stop, flush twice to drain, sponge remaining water from tank and bowl into the bucket, disconnect the supply line, unscrew the closet bolt nuts, and lift the toilet straight up — set it aside on cardboard or towels. Stuff a rag in the open waste line to block sewer gas.
Step 2: Remove the old flange
PVC/ABS flange: Use a flange chisel or putty knife to scrape off the wax ring residue. Cut the flange free with a multi-tool oscillating saw, removing just the flange — don't cut into the waste pipe. Inspect the remaining pipe for damage; if intact, you'll glue a new flange onto it.
Cast iron flange: Use a "spot repair" stainless steel ring that drops into the existing cast iron flange and bolts down — avoids removing the cast iron. The repair ring costs $20-35 and works for most cast-iron flange failures. If the cast iron itself has rusted through, you'll need a plumber and a section of cast-iron replacement.
Step 3: Install the new flange
For PVC: dry-fit first, mark the orientation so the closet bolt slots align perpendicular to the wall. Apply PVC primer (purple) to both surfaces, then PVC cement (clear or yellow), push together with a quarter-turn, hold for 30 seconds. Cement sets in 2 minutes, full cure in 30. The flange must sit flat on the finished floor — not below it (causes wax-ring failure) and not above it by more than 1/4 inch (causes rocking).
Step 4: Install closet bolts and wax ring
Drop new 5/16" closet bolts into the flange slots, secure with plastic retainer washers (most flanges include them). Place the wax ring on the flange (wax up, plastic horn pointing down into the drain). Some installers prefer placing the ring on the toilet horn — either works; flange-side is the more common modern technique.
Step 5: Set the toilet and tighten
Lower the toilet straight down onto the flange, aligning the bolts through the base holes. Press straight down with full body weight — you'll feel the wax compress. Don't rock or twist (breaks the wax seal). Hand-tighten the nuts alternately, then wrench another 1/4 turn each side. Stop the moment the toilet is firm. Over-tightening cracks the porcelain.
Step 6: Reconnect and test
Reconnect the supply, open the angle stop, allow tank to fill, flush 3 times while watching the base for any seepage. Re-caulk the base perimeter (skip the back 2 inches so future leaks are visible).