Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
Summary
A toilet tank that fills past the overflow tube keeps sending water down the drain long after the flush is done, and it usually reads to the household as "the toilet is running" or a water bill that crept up for no obvious reason. The fix is almost always a small adjustment at the fill valve, the part inside the tank that lets water back in after a flush and shuts off again once the tank is full. EPA's WaterSense program, which publishes water-efficiency guidance for toilets, tells facility staff to check that the refill water level sits below the top of the overflow tube and to lower the float if it does not. The same float that runs too high when it is set wrong can also be set too low, which shows up as a weak or incomplete flush instead of a running one.
What this page will not do is give you one exact water level for every toilet, because fill valve makers print their own target line on the valve, and it is not the same distance below the overflow tube from one brand to the next. So this page teaches you to find the mark inside your own tank first, and gives EPA's general guideline only for when no mark exists. It covers the common screw, dial and clip adjusters, and tells you plainly when a fill valve's design puts the job outside a simple adjustment, at which point the honest answer is to read that valve's own instructions rather than guess.
Necessary equipment
| Item | Note |
|---|---|
| Flashlight optional | Use the flashlight to read the mark inside the tank. |
| Mobile phone with a camera optional | Use the camera to record the make and the model of the valve. |
| Flat screwdriver optional | Some fill valves use a flat screwdriver on the adjustment screw. |
Look at the water level
Estimated 3 min
Source: WaterSense at Work: Sanitary Fixtures and Equipment — 3.1 Toilets (Water Closets) · tier 1 · accessed 2026-08-04
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
PUT THE TANK LID ON THE FLOOR, CLEAR OF YOUR FEET.
The lid is heavy china. A cracked lid has sharp edges that can cut your hand.
- Remove the tank lid with two hands.<1mReport a problem with step 1, Look at the water level
- Look at the water while the tank is full.<1mReport a problem with step 2, Look at the water level
- Find the overflow tube in the middle of the tank.<1mReport a problem with step 3, Look at the water level
- Extra water goes to the bowl through the overflow tube.
- This happens only when the tank is too full.
- Look at the fill valve and the overflow tube for a printed mark.<1mReport a problem with step 4, Look at the water level
- Some fill valves print their own target level on the body.
- Use the mark on your own fill valve as the target, if it has one.<1mReport a problem with step 5, Look at the water level
- If there is no mark, aim for one inch below the top of the overflow tube.<1mReport a problem with step 6, Look at the water level
- If water runs into the open top of the overflow tube, the level is too high.<1mReport a problem with step 7, Look at the water level
- If the bowl does not clear well after a flush, the level is likely too low.<1mReport a problem with step 8, Look at the water level
Find the adjuster on the fill valve
Estimated 1 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Look at the top of the fill valve for a screw or a dial.<1mReport a problem with step 1, Find the adjuster on the fill valve
- Look at the vertical rod inside the valve for a spring clip.<1mReport a problem with step 2, Find the adjuster on the fill valve
- The clip holds a float cup on the rod.
- If the fill valve has no screw, no dial and no clip, stop this procedure.<1mReport a problem with step 3, Find the adjuster on the fill valve
- Some fill valves reset their height when you unlock and move the whole body.
- Read the instructions for your fill valve, or fit a valve with an adjuster.
Adjust the water level
Estimated 4 min to 8 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
DO NOT FORCE THE SCREW OR THE DIAL.
A cracked valve body can leak or fail to close.
- Turn the screw or the dial a small amount.<1mReport a problem with step 1, Adjust the water level
USE YOUR FINGERS ON THE CLIP, NOT A TOOL.
A tool can pinch your fingers against the valve body.
- If your valve uses a clip, squeeze it and slide the float cup instead.<1mReport a problem with step 2, Adjust the water level
- Flush the toilet. Let the tank fill.1mReport a problem with step 3, Adjust the water level
- Compare the new level with your target.<1mReport a problem with step 4, Adjust the water level
- If the level moved the wrong way, turn the adjuster the opposite way.<1mReport a problem with step 5, Adjust the water level
- Repeat the small adjustment and the flush until the level matches your target.1mReport a problem with step 6, Adjust the water level
Do the final check
Estimated 1 min
- Flush the toilet again. Look at the level.<1mReport a problem with step 1, Do the final check
- Look at the top of the overflow tube for water.<1mReport a problem with step 2, Do the final check
- If the toilet still runs when you finish, stop. The fill valve needs a replacement.<1mReport a problem with step 3, Do the final check
Finish the job
Estimated under a minute
- Install the tank lid with two hands.<1mReport a problem with step 1, Finish the job
Terminology
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
- fill valve
- Also called: ballcock, ball cock, float valve, filler valve, refill valve, the float thing, the fill valve assembly
- overflow tube
- Also called: overflow pipe, standpipe, the open tube in the middle of the tank
- float
- Also called: float cup, float ball, the floating part
- water level
- Also called: fill level, refill level, tank water level, how full the tank is
- running toilet
- Also called: toilet keeps running, toilet won't stop filling, toilet hisses, phantom flush
When to use a professional
Stop if the toilet still runs after you adjust the float. The fill valve needs a replacement. This page does not cover that job.
Stop if the fill valve has no screw, no dial and no clip. Read the instructions for your fill valve, or fit a valve that has an adjuster.
Stop if the tank or the bowl has a crack. Speak to a plumber.
This page does not give one water level for every toilet. Use the mark on your own fill valve, if it has one. If not, use the guideline given in this page.
Common questions
Why does my toilet tank keep filling past the overflow tube?
The float inside the fill valve is telling the valve to keep filling even after the tank has enough water, so the extra spills into the overflow tube and straight down the drain. EPA's WaterSense program's own maintenance guidance for tank-type toilets says to check that the water level is set correctly and, as a general rule, keep the refill level about one inch below the top of the overflow tube. If it is set higher than that, lower the float; EPA's own guidance is that if the toilet still runs after the float is adjusted, the fill valve itself needs replacing.
Why does my toilet flush weakly or not clear the bowl?
A tank that is not filling high enough is one common cause of a weak flush, alongside a worn flapper or a partly closed stop valve. Korky, which makes replacement fill valves, warns that a fill valve set too low simply will not put enough water in the tank, leading to a weak or incomplete flush. Raise the float a little, flush, and check whether the bowl clears fully, repeating until it does.
How do I know what kind of adjuster my fill valve has?
Look at the top of the valve for a screw or a turning dial, and look at the vertical rod for a spring clip that grips a float cup. Some valves, including several of Korky's own replacement models, instead set the tank water level by unlocking and repositioning the whole valve body, so there is no separate screw or dial to turn. If you cannot find any of these, the safest step is to read the instructions that came with your fill valve, since the mechanism genuinely differs between manufacturers and even between generations of the same brand.
Is there one correct water level for every toilet tank?
No. Manufacturers print their own target line on many fill valves, and it is not always the same distance below the overflow tube. Korky's own instructions for its replacement valves put the mark at about half an inch below the top of the overflow tube, while EPA's general guidance for tank-type toilets uses about one inch as the rule of thumb when no mark is printed. Use the mark on your own valve first, and fall back to the general guideline only when there is none.
Is a running toilet from a high water level the same problem as a leaking flapper?
No, and telling them apart matters because the fix is different. EPA's WaterSense program attributes most silent toilet leaks to an old or worn flapper that lets water seep from the tank into the bowl even with the tank full. This page is about a different cause: a fill valve whose float is set too high, so water runs continuously into the overflow tube and down the drain, which a dye test built to catch a flapper leak will not show. If your tank water sits well below the overflow tube and the toilet still runs, check the flapper instead.
Do I need to turn off the water to adjust the water level?
Not for a fill valve with a screw, a dial or a clip: you can adjust those with the tank full and the water supply left on. A fill valve that sets its height by unlocking and repositioning the whole body is a bigger job, and this page does not cover it step by step. Follow the instructions for that valve, or have it replaced with one that has a simple adjuster.
Related procedures
- How to replace a worn toilet flapper when the toilet runs, ghost flushes, or leaks silently into the bowl
- How to tell if you have a hidden water leak using your water meter
- How to flush a water heater
- How to unclog a slow or blocked drain in a sink, bathtub or shower
- How to fix a leaky faucet that drips from the spout or weeps around the handle
- How to clean a clogged faucet aerator when the water flow drops or sprays sideways
- How to find and record the model and serial number of every appliance in the house
Sources
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
- Tier 1WaterSense at Work: Sanitary Fixtures and Equipment — 3.1 Toilets (Water Closets)
- Tier 1How to Replace Toilet Fill Valve
- Tier 1Residential Toilets
Revision history
Current version 1 · updated 2026-08-04 · next review due 2027-08-04
- v1 · 2026-08-04First draft. Overflow-tube check and the one-inch general target from EPA WaterSense at Work (2023, Section 3.1 Toilets); the height-adjustment mechanism, the too-high and too-low consequences, and the specific half-inch mark from Korky's own fill valve installation instructions. No single water level, adjustment direction, or reset method for a fixed-height valve publishes as a verified value, because all three differ by manufacturer and model. Written independently in Simplified Technical English; Fluidmaster's own instructions were sought but blocked automated access (HTTP 403) on every attempt, so no Fluidmaster source is cited.
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Comments and corrections
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.