How a toilet tank works
When you flush, the flapper at the bottom of the tank lifts and water rushes into the bowl. The flapper drops back, and the fill valve refills the tank until a float tells it to stop. A small tube from the fill valve also refills the bowl through the overflow pipe.
Most running toilets come down to one of those parts: a flapper that no longer seals, a fill valve that does not shut off, or a float set so high that water spills into the overflow. Hard water deposits can make flappers stiff and valves sticky over time.
Symptoms and likely causes
| Symptom | Likely cause | Usual fix |
|---|---|---|
| Tank refills briefly every so often | Flapper leaking into the bowl | Replace the flapper |
| Water runs into the overflow tube continuously | Float too high or fill valve not shutting off | Adjust the float or replace the fill valve |
| Hissing sound from the tank | Fill valve seat worn or debris in the valve | Clean or replace the fill valve |
| Water on the floor around the base | Wax ring seal failed or loose closet bolts | Pull the toilet and reset with a new seal |
| Drips from under the tank | Tank-to-bowl gasket or bolt washers | Replace the gasket and bolts |
| Supply line wet | Worn supply hose or loose connection at the stop valve | Replace the supply line |
Stop the water first
- Close the toilet's stop valve.It is on the wall or floor behind the toilet, below the tank. Turn it clockwise until snug.
- Flush once.This empties the tank so you can see inside and reduces the water that can leak.
- If the stop valve will not close.Do not force it. Close the main water shutoff and note the stuck valve for repair.
When to call a plumber
- IfOnly the flapper or fill valve is at fault and the stop valve worksThenMany homeowners replace these parts themselves following the part's instructions.
- IfWater appears around the base or the toilet rocksThenCall a plumber. The seal needs resetting and the flange or subfloor should be checked.
- IfThe stop valve is stuck, seeping or corrodedThenHave it replaced before it fails during a repair.
- IfThe toilet clogs often or other drains gurgle when it flushesThenThe problem may be in the drain line, not the toilet.
Questions to ask
- Is the flange under the toilet in good condition?
- Is there any sign of water damage to the subfloor?
- Should the stop valve and supply line be replaced at the same time?
- Is this toilet worth repairing, or would replacement make more sense?
Common questions
Why does my toilet run for a few seconds by itself?
That is often called a phantom flush. Water is slowly leaking past the flapper, and the fill valve tops the tank back up.
Can I just tighten the bolts if the base leaks?
Overtightening can crack the porcelain, and a failed wax seal will not reseal by tightening. The usual fix is pulling the toilet and installing a new seal.
Does a running toilet affect my water bill?
Yes. A continuously running toilet can use a large amount of water. The meter test on this site can confirm it.
General information for Golden Hills, not a quote or professional advice. In an emergency, call 911.