Quick Answer:
If a toilet keeps running after you turn the water back on following a shutoff, start by opening the shutoff (stop) valve all the way and flush the toilet a few times to clear trapped air. If the float or arm is sticking, gently move it by hand to seat the fill valve. If the float continues to stick or the fill valve won’t stop, the fill/flush valve likely needs replacement or a plumber’s help.
Why This Happens
When water is shut off and then restored, air can get trapped in the supply line and in the tank. That air can cause the fill valve to behave irregularly until it’s pushed out. Mechanical parts in the tank — the float, float arm, fill valve or flapper — can also be sticky or misaligned after being idle. Worn or failing fill valves may not reseat correctly and will let water run continuously.
These problems are common and often temporary, but if the system won’t settle you may see issues similar to Toilet runs longer than normal or situations that happen when service work is done, like Toilet runs after replacing main shutoff.
Step-by-Step What to Do
1. Open the stop valve fully
- Turn the angle stop (the small valve under or behind the toilet) all the way open. A partially open shutoff can cause irregular flow that confuses the fill valve.
2. Cycle the toilet a few times to clear air
- Flush the toilet 2–3 times in a row. Let the tank refill fully between flushes. This helps push trapped air out of the line and lets the fill valve settle.
3. Check the float and gently free it if needed
- Open the tank lid and watch the fill process. If the float rises then drops or hangs and doesn’t let the valve close, reach in and gently move the float or float arm to make sure it moves freely.
- If it’s a modern cup-style float on the fill valve, push it up and down lightly to free any binding.
4. Inspect the flapper and valve if running continues
- If the toilet still runs after freeing the float and cycling, check that the flapper seals well and the fill valve is seating. Mineral build-up or worn parts often cause persistent running.
- Persistent float sticking or a fill valve that won’t close usually means it’s time to replace the valve assembly.
5. If you can’t stop it, shut off supply and get help
- If the toilet won’t stop running and you can’t diagnose it, turn the shutoff valve off to stop water waste and contact a plumber.
What Not to Do
- Don’t bang on the float or valve to “unstick” it—this can crack parts; if it keeps sticking, a plumber is appropriate.
- Don’t force or bend plastic parts; forcing can break a float arm or crack the tank components.
- Avoid pouring strong chemical cleaners into the tank to try to fix mechanical sticking; they won’t fix a bad valve and can damage parts.
When to Call a Professional
- The toilet still runs after you’ve opened the shutoff fully, cycled flushes and freed the float.
- You cannot stop the water flow because the shutoff valve is stuck or leaks.
- You suspect the fill valve or internal assembly is damaged or corroded and you’re not comfortable replacing it yourself.
Safety Notes
- Work with the shutoff closed if you need to disassemble internal parts. Keep a bucket and towels handy for water spills.
- Don’t use excessive force on plastic components; they can break and cause leaks that are harder to fix.
- If you smell gas, have electrical problems, or if leaked water is affecting electrical outlets, stop and call a professional immediately.
Common Homeowner Questions
- Q: How many flushes should I do to clear the air?
A: Usually 2–3 full flushes will clear most trapped air. - Q: Can I replace the fill valve myself?
A: Yes—replacing a fill valve is a common DIY task if you’re comfortable with basic tools; turn off the supply first and follow the part’s instructions. - Q: Will the problem fix itself after a few hours?
A: Sometimes air clears and the valve settles, but if the float or valve sticks repeatedly, it likely needs repair or replacement.
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