A toilet that still runs after you cleaned the fill valve usually has one of four problems: the valve cap or refill tube was put back wrong, the float height is too high, the valve seal is worn, or the leak was never the valve at all and is a flapper. A water-off test tells you which.
First, where is the water going?
Take the lid off and watch the tank after it fills. This one look splits the problem in two.
Water is spilling into the overflow tube and the fill valve never shuts off. That is a fill valve problem: height, cap, tube or seal. Fluidmaster puts it this way: if the water level rises so high it drains into the overflow pipe, follow the steps for cleaning the fill valve, and if that does not resolve it, replace the fill valve.
The tank stays full and the water level sits below the overflow tube, but the valve kicks on every few minutes. Now the leak is downstream. Korky explains that a worn flapper or flush valve seal lets water slowly leak from the tank into the bowl. As the tank level drops, the float drops and turns the water back on. The valve you cleaned was fine.
The water-off test settles it
Do this before you buy anything.
- 1Flush, let the tank refill, and mark the water level inside the tank with a pencil.
- 2Turn the supply valve off.
- 3Wait. Korky says to wait at least 25 minutes. Fluidmaster says 10 to 15 minutes and then check whether the level has dropped from your mark.
If the level drops with the water off, a tank part is leaking, and the fill valve is not the problem. Fluidmaster says to replace the flapper first because it is the most common cause. Korky adds that if the level falls only as far as the flapper or flush valve seal, replace the flapper or seal, and if it falls to a point on the overflow tube or the bottom of the tank, the flush valve needs replacing. If the level holds steady with the water off, the leak is the fill valve, so read on.
Four things that go wrong after cleaning a fill valve
1. The cap is not locked on. Fluidmaster's flushing procedure has you twist the cap and arm 1/8 turn counterclockwise to release it, and to lock it again you press the cap down while turning it clockwise. If you only set the cap on top, take it off and relock it.
2. Debris is still in the inlet. Fluidmaster's steps: with the cap off, hold an upside-down cup over the open valve body, turn the supply on full for 10 to 15 seconds, then look inside to make sure no debris is left. Fluidmaster's maintenance sheet adds that you should do the rinse twice. Phoenix water is hard, roughly 10 to 17.6 grains per gallon in the city's water quality report, so expect mineral buildup as well as grit. Kohler notes that sediment in the cap is a common cause of constant running, especially after a new installation, when turning the water supply on and off can loosen sediment in the lines.
3. The refill tube is in the wrong place. Korky's troubleshooting steps say to make sure the refill tube is not pushed into the overflow tube, because that can create a siphon. Attach it the way the maker shows for your flush valve, clipped or pressed in at the top, not pushed down inside.
4. The float or valve height is set too high. Korky says that when a valve is set too high it will not shut off and risks running constantly or overflowing. Its guide puts the water level mark on the valve about 1/2 inch below the top of the overflow tube. Lower the float, or reset the valve height, and watch a full refill.
The seal may be worn even if the valve is clean
If the cap is locked, the tube is clipped right, the height is right, and the flush-out is done, the rubber seal under the cap may simply be worn. Fluidmaster identifies the seal as the rubber disc with a pin coming through, and sells a replacement seal and a replacement top cap assembly. It says working parts can start to wear out on valves in use for 7 years or more. Korky puts typical fill valve life at 5 to 7 years, depending on your water. Kohler's advice is the same in short form: replace the fill valve if the toilet is still constantly running after flushing it.
If you replace the valve, Fluidmaster versus Korky helps you choose, and how to replace a toilet flapper or fill valve walks through the swap.
Trim chain slack before you quit
While you have the lid off, check the flapper chain. Kohler suggests roughly one to two links of slack so excess chain does not get caught on the trip lever arm, and Korky recommends the same. A chain that is too tight can keep the flapper from sealing, and the water-off test above will catch that.
When to stop and call a plumber
Stop DIY when the supply shutoff valve will not close or weeps at the stem, the tank or bowl is cracked, the toilet runs again within weeks of a new valve and flapper, or you cannot tell which part is leaking. That last one is worth a visit, because a running toilet wastes water around the clock. HQ Plumbing and Air handles toilet repair in the Phoenix area, and we give you the price before the work starts. For the broader checklist, see how to fix a running toilet and why a toilet flushes on its own.