Quick Answer:
If your toilet starts running after the city water comes back on, chances are gritty sediment or a displaced refill tube kept the fill valve from seating. Before replacing parts, flush a nearby faucet to clear lines, then check the fill valve inlet screen and refill tube for debris and proper placement.
Why This Happens
When the city water supply is interrupted, sediments that normally sit in the main line can shift. When service resumes those particles move through your plumbing and can collect at narrow points: the small mesh screen at the fill-valve inlet, the refill tube, or where the float seals. Sediment or grit can prevent the valve from seating cleanly, causing a slow or constant run.
You may also see temporary pressure surges that move the float or kink the refill tube. If the running stops after you clear the particles, the problem was likely just debris rather than a failed valve or seal. This is similar to other situations like Toilet runs after winterization and localized fixtures such as Toilet runs only upstairs bathroom, where water-disturbance or local plumbing differences cause one fixture to behave differently.
Step-by-Step What to Do
1. Flush a nearby faucet first
- Open a cold-water faucet on the same supply line (usually a sink on the same floor). Let it run for 30–60 seconds to push any loose sediment out of the house piping.
- If water is discolored or sandy, run the faucet until it clears before working on the toilet.
2. Stop the toilet and inspect
- Shut the toilet’s shut-off valve (located behind the tank) and flush to empty the tank.
- Remove the tank lid and set it somewhere safe.
3. Check the fill valve inlet screen
- Look where the supply hose connects to the fill valve. There’s often a small mesh screen inside the metal or plastic fitting.
- If you see grit or buildup, place a bucket under the valve, disconnect the supply hose, and rinse the screen gently with clean water or brush it with an old toothbrush. Don’t poke hard with metal tools.
4. Inspect the refill tube and valve internals
- Check the refill tube (the small hose from the fill valve to the overflow tube) for blockages, kinks, or pieces of debris.
- If the refill tube is clogged or soft with sediment, replace it; they’re inexpensive and simple to swap.
- With the valve reconnected, turn the supply back on slowly and watch for proper fill and shutoff.
5. Test and adjust
- Let the tank fill and observe whether the valve seats fully and stops the flow. If it still runs, gently adjust the float height or the fill-screw per the valve type.
- Cycle the toilet once after you’ve flushed the nearby faucet and cleaned screens. If the run stops, monitoring for a day is usually enough to confirm the issue is resolved.
What Not to Do
- Don’t keep cycling the toilet right after an outage without flushing sediment first—grit can damage seals and make the problem worse.
- Don’t stick metal picks or sharp tools into the fill valve or valve seat; you can nick the seal and create a lasting leak.
- Don’t assume immediate replacement of the whole valve is necessary; often cleaning the inlet screen and refill tube fixes it.
- Don’t pour strong chemicals into the tank to “clear” sediment; they won’t reach the valve screen and can damage rubber parts.
- If the issue persists after these checks, calling a plumber is appropriate rather than continuing to force fixes yourself.
When to Call a Professional
- If you cleaned the inlet screen and refill tube and the toilet still runs constantly.
- If the valve leaks at the supply connection or the valve body looks cracked or worn.
- If you’re uncomfortable shutting off or disconnecting the supply, or you suspect a pressure problem in the house lines.
Safety Notes
- Turn off the toilet shut-off valve before disconnecting the supply hose to avoid water spills. Keep towels or a small bucket handy.
- Avoid using metal tools inside plastic valve components to prevent cracking. Use gentle rinsing and a soft brush.
- If water is discolored after an outage, avoid drinking it until it runs clear. Flushing lines first reduces sediment that can damage fixtures.
Common Homeowner Questions
- How long should I run a faucet after service returns? Run it until water clears—usually 30–60 seconds; longer if it’s discolored.
- Can I replace the fill valve myself? Yes, many homeowners can replace a fill valve; turn off water, drain the tank, and follow the part instructions. Stop and call a pro if you find cracked fittings or uncertain connections.
- Will sediment damage other fixtures? It can; filters and screens in other fixtures may clog, so flush nearby taps and check appliance intakes if you notice issues.
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