Quick Answer:
If your toilet started refilling or running after you turned the water back on, it’s usually air or small debris in the lines stopping the flapper from seating. Purge the air at faucets, then retest the tank seal and flapper operation before assuming a part has failed.
Why This Happens
- When water is shut off for repairs, air enters the supply lines. That air — or grit that came loose during work — can travel to the toilet tank and stop the flapper or seat from sealing cleanly.
- A flapper that’s hit by grit may rock just enough to let water trickle past. If the refill valve senses that trickle, it refills and the tank appears to run intermittently.
- If the problem began after adding a smart shutoff or changing hardware, related components can affect pressure and seals; check related documentation like Phantom refills after installing smart shutoff or, if you recently replaced the fill valve, see Random refill after replacing fill valve.
Step-by-Step What to Do
1. Stop continuous flow into the tank
- Close the toilet’s angle stop (the small shutoff at the toilet base) so you don’t waste water while you check things.
2. Purge the air from the plumbing
- Open cold faucets one at a time, starting at the lowest plumbing fixture in the house (basement or first floor) and work upward to the highest. Open both cold and hot where needed until the flow runs steady and stops sputtering.
- Open outdoor spigots if present; they help push air out of the system.
- Run each faucet for a minute or two until the stream is steady and clear.
- Be careful with hot water — open hot taps only briefly until you confirm the temperature is safe.
3. Clear the toilet tank and inspect the flapper
- With the water still off to the toilet, remove the tank lid and visually inspect the flapper and seat for grit, debris, or misalignment.
- If you see debris on the seat, lift the flapper and rinse it under a faucet or wipe the seat with a clean cloth.
- Check the chain length: it should have a little slack but not so much that it catches under the flapper.
4. Restore water and retest the tank sealing
- Slowly open the toilet angle stop to allow the tank to refill. Opening slowly reduces more air entering the fixture.
- Flush once or twice and watch the flapper seat. Listen for hissing or a steady trickle that indicates a poor seal.
- If the tank now seals and stops refilling, you’ve likely cleared the air/grit issue. If not, proceed to the next checks.
5. Next checks if it still runs
- If the flapper looks damaged, replace it — flappers are inexpensive and easy to swap.
- If the fill valve continues to cycle or water level is erratic, the fill valve may be faulty or clogged and might need cleaning or replacement.
What Not to Do
- Don’t cycle the main shutoff repeatedly. Rapidly opening and closing the main valve can introduce more air and stress the system.
- Don’t assume additional force or improvised fix will help; avoid forcing the flapper or jammed parts in place.
- If air or debris continues to cause problems after purging and basic cleaning, don’t keep trying quick fixes — call a plumber if air/debris continues.
When to Call a Professional
- There’s a persistent leak or phantom filling after you’ve purged lines and cleaned the flapper.
- Water pressure is erratic throughout the house, or multiple fixtures act up after the shutoff — this can indicate a larger supply issue.
- You’re not comfortable removing or replacing valves or flappers, or you suspect internal damage to the fill valve assembly.
Safety Notes
- Protect floors when working inside the tank; lay down towels to catch drips.
- When purging hot water lines, test the water temperature before fully opening taps to avoid scalding.
- Use only gentle force when handling tank parts; plastic components can break if over-tightened.
Common Homeowner Questions
- Will air in the lines damage my toilet? — No. Air usually only causes sputtering or sealing issues, not permanent damage.
- How long should I run faucets to purge air? — A few minutes per fixture, or until flow is steady and free of spluttering.
- Can I fix this myself? — Often yes: purging and cleaning the flapper fixes most cases. Call a plumber if it keeps happening or components look damaged.