Quick Answer:
If a toilet starts running after nearby plumbing work, the most common causes are grit or debris pushed into the supply line or a disturbed shutoff/valve. First check the flapper and fill valve operation, then briefly flush the toilet stop valve to clear any debris and inspect the fill valve screen if you can access it. If the valve is old or stuck, or if debris looks trapped inside the fill valve, call a plumber.
Why This Happens
Work on nearby pipes can stir up sediment or small bits of scale. That material can travel through the supply line and lodge in the fill valve or its inlet screen, preventing the valve from shutting off cleanly. Also, the supply stop (shutoff) may have been moved or partly closed and reopened during the job, leaving grit in the line or a valve that’s not seating like it did before. These problems are similar to other pressure or supply disturbances such as Toilet runs when water heater kicks on and Toilet runs after city outage where changes in flow and pressure move debris around.
Step-by-Step What to Do
1. Watch and confirm the problem
- Lift the tank lid and flush once. Observe whether water keeps running into the tank after it should stop. Note whether the flapper seals fully or if water is trickling past it.
- Look for the simpler causes first: chain caught under the flapper, misaligned flapper, or a cracked flapper.
2. Test the supply stop (brief flush)
- Locate the shutoff valve under the tank. Gently close it just until flow stops, hold briefly (a few seconds), then open it again. This “flush” of the stop can move loose grit through the valve and out into the supply so it doesn’t sit at the fill valve inlet.
- Do this gently—do not force a stiff or corroded valve. If the valve is hard to move, skip this and call a pro (see What Not to Do).
3. Check the fill valve screen (if accessible)
- Turn off the supply and flush to drain the tank. Many fill valves have a removable top or a mesh screen where the supply nut connects. If yours is easy to access, look for grit and rinse it away.
- If the screen or valve top is not clearly removable, or you’re unsure, stop here and contact a plumber rather than forcing parts apart.
4. Verify flapper and float settings
- After clearing any visible grit and restoring water, watch another flush. Make small float adjustments if water level is too high (it should be about 1 inch below the overflow tube).
- If the flapper still won’t seat, replace the flapper—this is a cheap and common fix.
5. Replace the fill valve if needed
- If cleaning the screen and flushing the stop fixed nothing and the valve still leaks or won’t shut off, replacing the fill valve is often the next step. If you’re not comfortable, have a plumber do it.
What Not to Do
- Don’t force old stop valves after repairs—they can break. A broken valve under the tank can cause a leak that’s harder and more expensive to fix.
- Don’t strip or pry apart a fill valve that wasn’t designed to be opened. If you suspect debris is inside the fill valve itself, a plumber is appropriate.
- Don’t leave the tank lid off where it can fall and break; handle it carefully and set it somewhere soft while you work.
When to Call a Professional
- The running continues after you gently flush the shutoff and check the screen and flapper.
- The shutoff valve is stiff, corroded, or you’re worried you might break it by moving it.
- You see multiple fixtures affected, or there’s ongoing debris in other lines—this can indicate larger work was done that left sediment in the system.
- You’re not comfortable accessing the fill valve or unsure how to reassemble components safely.
Safety Notes
- Turn off the shutoff before putting your hands inside the tank. Wear gloves to keep things sanitary and to avoid sharp edges on old hardware.
- Avoid metal tools directly on porcelain; use towels or a soft pad to protect the tank lid and surfaces.
- If you smell sewer gas or see overflowing water you can’t stop, close the main house valve and call a plumber immediately.
Common Homeowner Questions
- Will debris clear itself over time? Often small debris will move on the next use, but if the valve keeps running repeatedly, manual flushing of the stop and cleaning the screen is recommended.
- Can I replace the fill valve myself? Yes, many homeowners can replace a fill valve with basic tools, but call a plumber if you’re unsure or the shutoff is fragile.
- Could the plumber have left something loose? Yes, it’s possible. If you suspect the recent work caused the issue and simple checks don’t help, contact the contractor who did the work or a plumber to inspect.
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