Fix a Running Toilet (Flapper + Chain)

Stop the constant refill by installing a fresh flapper and setting the chain for a clean, reliable seal.
Difficulty: Very Easy
Success Rate: 90%
Cost: $6 - $15
Estimated Timeline: 10–20m
Turn Off Water: Yes
Find a Local Plumber
Tools Needed:

  • None required (optional: scissors or snips)

  • Small towel or sponge

  • Flashlight

Materials / Parts:

  • Replacement flapper (match valve size/brand or use universal adjustable)

  • New chain with clip (usually included with flapper)

Safety Warnings:

  • Porcelain can chip—avoid hard tools inside the tank.

  • Do not use toilet tank drop-in cleaners; they degrade rubber parts.

Test & Verify:

  • With the handle untouched, watch the water at the flapper seat—no ripples after 60–90 seconds.

  • Add a few drops of food coloring to the tank; wait 5–10 minutes. No color should appear in the bowl.

  • Listen for silent fill—no periodic refills.

Cleanup & Disposal:

  • Wipe the tank rim and lid; replace lid carefully.

  • Dispose of the old flapper in household trash.

Pre-Checks:

  • Lift the tank lid and confirm water is trickling into the bowl or down the flush valve.

  • Note flapper style/size (2″ or 3″) and hinge attachment type.

  • Check the overflow tube height and that the refill tube is clipped above the tube—not pushed down inside.

Step-By-Step Instructions:

  1. Turn the shutoff valve clockwise to stop water; flush to empty most of the tank.

  2. Hold the flapper open to drain remaining water; use a towel to dab up puddles.

  3. Unclip the old chain from the handle lever; detach the old flapper from the valve ears or posts.

  4. Clean the flush valve seat with a towel; remove any slime or mineral grit.

  5. Install the new flapper on the valve ears/posts; ensure hinges sit flat and pivot freely.

  6. Clip the new chain to the handle lever, leaving about 1/4–1/2 inch of slack—no kinks, no constant tension.

  7. Turn water back on; let the tank fill fully.

  8. Test flush: the flapper should lift freely and fall back to seal. Adjust chain one link at a time if it hangs up or won’t seal.

  9. If using an adjustable flapper, fine-tune the flow setting per instructions to stop short-cycling while still getting a good flush.

  10. Verify the refill tube is clipped above the overflow tube and not inserted into it.

When to Stop & Call a Pro:

  • The flush valve seat is warped, cracked, or pitted and won’t seal.

  • The shutoff valve leaks or won’t turn.

  • Water continues to run despite correct chain slack and a new flapper.

Common Mistakes:

  • Chain too tight (flapper can’t seal) or too loose (flapper won’t open fully).

  • Using the wrong flapper size/type for the valve.

  • Refill tube shoved down the overflow, causing siphoning and periodic refills.

  • Skipping seat cleaning so grit holds the flapper open.

Troubleshooting:

Q: Dye test still shows color in the bowl.
A: Shorten the chain one link; ensure the flapper hinge sits flat; replace with brand-specific flapper if universal won’t seal.

Q: Flush is weak after replacement.
A: Chain may be too long; shorten so the flapper lifts fully without binding.

Q: Runs only sometimes, usually at night.
A: Water level may be set too high and spilling into the overflow; lower the fill valve level about 1/2 inch below the top of the overflow tube.

Q: Handle sticks down after flushing.
A: Reposition the chain to avoid rubbing on the lever or overflow; ensure the handle nut isn’t overtightened.