Toilet runs only upstairs bathroom

Upstairs bathroom toilet running while other toilets are fine.

Quick Answer:

If only the upstairs toilet keeps running, start by treating it as a single-toilet problem: compare its behavior to a downstairs toilet, make sure the supply stop valve at the wall is fully open, then inspect and adjust the float and the flapper seal inside the tank. Often the fix is a simple adjustment or a worn flapper/fill valve replacement rather than a whole-house issue.

Why This Happens

A toilet that runs by itself usually means water is escaping from the tank into the bowl or the tank can’t refill properly. Common causes that affect one fixture and not others include:

  • Worn or warped flapper that won’t seal the flush valve.
  • Float or fill-valve misadjustment so water constantly overflows into the overflow tube.
  • Partially closed or malfunctioning supply stop at that toilet, limiting refill flow and confusing the valve mechanism.
  • Mineral buildup or age-related wear in the fill valve or flapper parts unique to that toilet’s tank.

Situations like recent winterization or a slow internal leak can produce similar symptoms — for more background on related causes, see Toilet runs after winterization and Running toilet with no visible leak.

Step-by-Step What to Do

Step 1 — Compare to another toilet

  • Flush a working downstairs toilet and the upstairs one. Note refill speed, noise, and whether the upstairs runs after the tank finishes filling.
  • If the downstairs fills normally and stops cleanly, you can focus on the upstairs tank parts rather than your home’s main supply or pressure.

Step 2 — Check the supply stop (angle stop)

  • Look at the shutoff valve on the wall behind the toilet. Turn it fully counterclockwise until it stops, then test a flush again. A partly closed stop can cause slow refill or repeated cycling.
  • If the valve leaks or won’t turn, stop and consider calling a plumber to avoid breaking it.

Step 3 — Inspect and test the flapper

  • Remove the tank lid. With the tank full, press down on the flapper to see if the running stops. If pressing it stops the run, the flapper likely isn’t sealing.
  • Look for mineral deposits, warping, or a brittle rubber seal. Replace the flapper if it looks worn — inexpensive and easy to swap.

Step 4 — Adjust the float and fill valve

  • Locate the float (ball or cup style). If the water level is above the overflow tube top, lower the float a little so the tank stops filling before water spills into the tube.
  • Most modern fill valves have a small clip or screw to adjust height. Make one small adjustment, then flush and observe.
  • If the valve keeps running despite adjustment, the fill valve may be failing and should be replaced.

Step 5 — Check the chain, handle, and overflow tube

  • Make sure the chain isn’t too short (holding the flapper slightly open) or tangled. Give it a little slack so the flapper closes fully.
  • Confirm the overflow tube is not cracked and that the normal water level sits about 1 inch below its top.

Step 6 — Test and repeat as needed

  • After each change flush and watch for at least a minute. A brief run may be normal while the tank refills; continuous or periodic cycling indicates the issue remains.
  • If part replacement is needed, toilet repair kits with a new flapper and fill valve are common solutions for a single running toilet.

What Not to Do

  • Don’t assume an upstairs-only running toilet means a whole-house plumbing problem — first focus on that toilet’s flapper, float, fill valve, chain, and stop valve.
  • Don’t force or over-tighten the shutoff valve if it won’t move; a broken stop can cause larger leaks. If access is tight or parts are hard to reach, a plumber is appropriate.
  • Don’t ignore a continuously running toilet — it wastes water and may hide a failing part that will leak later.

When to Call a Professional

  • The shutoff valve is seized or leaking when you try to use it.
  • Replacing basic parts (flapper, fill valve) doesn’t stop the running or the tank cycles continually.
  • There are signs of water damage on ceilings or walls below the upstairs bathroom, or you smell mildew — these indicate a leak beyond a simple running issue.
  • Limited access or unfamiliarity with toilet internals makes you uncomfortable performing the repair yourself.

Safety Notes

  • Turn off the toilet’s supply valve before replacing internal parts to avoid accidental flooding.
  • Remove the tank lid carefully — it’s heavy and fragile. Set it on a flat surface to avoid chips or breaks.
  • Use hand tools designed for plumbing; avoid excessive force on plastic parts to prevent cracking.

Common Homeowner Questions

  • Q: Can I wait to fix a running toilet?
    A: It’s best to fix it promptly — even intermittent running wastes water and can raise your bill.
  • Q: Is replacing the fill valve hard?
    A: For someone comfortable with basic tools it’s straightforward; kits and instructions are common, but call a plumber if you’re unsure.
  • Q: Could low water pressure upstairs cause this?
    A: Low pressure usually affects multiple fixtures; if only one toilet runs, the issue is typically internal to that tank.

For more related articles, see the nan hub.

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