Quick Answer:
If the tank keeps filling, first stay by the toilet so it doesn’t overflow. Try turning the toilet stop valve slightly closed to see if filling stops. If that doesn’t help, lift the tank lid and inspect whether the float is hung up or the fill valve is stuck open. If the fill valve won’t shut after simple checks, call a plumber.
Why This Happens
Most constantly filling toilets are caused by one of three simple problems: the fill valve is stuck open, the float that tells the valve to stop is caught or set too high, or the flapper at the bottom of the tank isn’t sealing and water keeps flowing into the bowl. Less commonly, a valve or valve seat is worn out. The immediate risk is an overflowing tank or water damage to the floor if the chain or valve fails while you aren’t watching.
Step-by-Step What to Do
1. Stay with the toilet and watch
Keep an eye on the tank. If water reaches the overflow tube, it will run into the bowl instead of overflowing the room, but don’t rely on that — standing by lets you act quickly.
2. Try the shutoff at the toilet
Locate the toilet stop valve (usually on the wall behind or beside the toilet). Turn it clockwise a quarter to half turn to close slightly. This will reduce or stop the water flow and confirms whether the supply is feeding the continuous fill. If closing it stops the filling, the issue is with the fill valve or float.
3. Inspect the float and fill valve
Remove the tank lid and look at the float and the fill valve assembly. Lift the float by hand and see if the water stops. Check whether the float is hung up on the overflow tube or the tank wall. Also look for debris or mineral buildup on the fill valve that can prevent it from closing.
4. Test and reset the fill mechanism
- If the float moves freely and lifting it stops water, adjust the float height per the manufacturer’s guidance so it shuts sooner.
- If the fill valve remains open when the float is lowered, try gently tapping or cleaning the valve. If that doesn’t close it, replacement is usually required.
5. Turn off the main water if needed
If you can’t stop the flow at the toilet stop valve or the tank is overflowing, shut off the house water main and call for help. Controlling the water supply prevents damage while you troubleshoot or wait for a plumber.
6. Consider related causes and next steps
If the trouble began after a recent repair, check that parts were installed correctly — for example, a misaligned flapper can let water leak. For more troubleshooting scenarios, see Running toilet after replacing flapper. If the problem seems to occur under specific conditions rather than all the time, compare notes with situations described in Toilet runs only at night.
What Not to Do
- Don’t leave a toilet that won’t stop filling unattended—there is a real overflow risk and potential water damage.
- Don’t try to force or permanently disable valves if you don’t know what you’re doing. If the fill valve won’t shut, a plumber is appropriate.
- Don’t ignore mineral buildup or loose parts; small leaks can waste a lot of water and worsen over time.
When to Call a Professional
- If the fill valve remains open after you’ve inspected and tried basic adjustments.
- When the toilet stop valve does not reduce or stop flow when turned.
- If you’re uncomfortable shutting off the water main or replacing parts yourself.
Safety Notes
- Always turn valves slowly and avoid overtightening; valve packing can break if forced.
- Protect the floor around the toilet with towels or a shallow pan if you expect overflow while working.
- If you shut off the house water, inform household members so fixtures aren’t unexpectedly used.
Common Homeowner Questions
- Why is the toilet still filling after I flush? The fill valve or float isn’t shutting off, or the flapper isn’t sealing; check those parts first.
- Can I fix a stuck fill valve myself? Often you can clean or replace a cheap fill valve, but call a plumber if you’re unsure or if the valve won’t stop.
- Will turning the stop valve off hurt anything? No—partially or fully closing the toilet stop valve is a safe first step to prevent overflow; if it doesn’t work, close the main water.
For more related articles, see the nan hub.