Toilet repair

A toilet runs constantly when the fill valve that lets water into the tank isn’t closing completely. A toilet runs intermittently because the valve opens slightly for a few minutes. In either case, you have to figure out why that valve isn’t stopping the incoming water flow. 

First, look for leaks. A leak in the tank can make a toilet run constantly or intermittently. If your toilet is leaking, you’ve probably noticed it already. But take a look just to be sure. If you find leaks coming from the tank bolts or flush valve, you’ll most likely have to remove the tank from the bowl so you can replace the tank bolts, the rubber washers and the gaskets on the flush valve. If there are leaks around the fill valve, tighten the locknut (see    Photo 6 - 7). Leaks can come from cracks in the tank, too, but in that case, the only reliable solution is a new toilet.

If you don’t find any leaks, lift off the tank cover. At first glance, the array of submerged thingamajigs inside may look intimidating, but there are really only two main parts: the flush valve, which lets water gush into the bowl during the flush; and the fill valve, which lets water refill the tank after the flush. When a toilet runs constantly or intermittently, one of these valves is usually at fault. 

Toilet cutaway 

 To determine which valve is causing the trouble, look at the overflow tube. If water is overflowing into the tube, there’s a problem with the fill valve.  If the water level is below the top of the tube, the flush valve is leaking, allowing water to trickle into the bowl. That slow, constant outflow of water prevents the fill valve from closing completely.

We cut away the fronts and backs of new toilets to show you how to replace these parts. Your toilet won’t look so pristine inside. You’ll find scummy surfaces, water stains and corrosion. But don’t be squeamish—the water is as clean as the stuff that comes out of your faucets.

Solution 1:   Repair or replace the fill valve

Fix 1:   Adjust the float or the fill valve
If your valve has a ball that floats at the end of a rod, gently lift the rod and listen. If the water shuts off, you may be able to stop the running by adjusting the float. Some fill valves have a float adjustment screw on top. If there is no adjustment screw, bend the float arm (Photo 1). 

                                                                                                 
1. Gently bend the float arm down to put extra pressure on the valve.

If you have a Fluidmaster-style fill valve, make sure it’s adjusted properly (Photo 2). Pinch the spring clip and slide the float down 1/4 inch, then release it and see if the water stops.  (You don’t have to empty the tank to make these adjustments.)                                          

2. Pinch the spring clip and slide the float up or down on the metal rod to change the water level.

Fix 2:   Flush the valve
Hard water, debris from old pipes or particles from a break in a city water line can prevent a flush valve from closing completely. Running water through it from the supply line will clear the debris.    Photos 3 and 4 show you how to do this on one common type of valve. Even though other valves will look different, the clearing process is similar. However, you may have to remove a few screws on top of the fill valve to remove the cap.

3. Remove the  fill valve cap. On this type of valve, press down and turn counterclockwise. Remove screws on other types of valves.

4.  Cover the valve with your hand. Turn on the water (cautiously, so you don’t get a cold shower!) and let it flush out the valve for a few seconds.

Fix 3:   Replace the washer
When you remove the cap to flush out the valve, inspect the washer for wear or cracks. Replacing a bad washer is cheap ($1) and easy (Photo 5). But finding the right washer may not be. The most common washers are often available at home centers and hardware stores. Other styles can be hard to find. If you decide to hunt for a washer, remove it and take it to the store to find a match. Plumbers usually replace the whole fill valve rather than hunt for a replacement washer.

5.  Replace a worn, cracked valve washer by prying the old washer out of the cap with a small screwdriver. Press the new one into place.

Fix 4:   If you can’t fix the fill valve, replace it
Replacing a fill valve requires only a few basic tools (an adjustable pliers and a pair of scissors) and an hour of your time. A kit containing the type of valve we show here and everything else you need costs about $12 at home centers and hardware stores.

Your first step is to shut off the water. In most cases, you’ll have a shutoff valve right next to the toilet coming either through the floor or out of the wall. If you don’t have a shut-off, turn off the water supply at the main shutoff valve, where water enters your home. This is a good time to replace the supply line that feeds your toilet if it's old with a flexible supply line reinforced with a stainless steel sleeve. Photos 6 - 12 show how to replace the valve. 

6. Turn off the water at the shutoff valve. Flush the toilet and hold the flush valve open to drain the tank. Sponge out the remaining water or vacuum it up with a wet/dry vacuum.

7. Unscrew the coupling nut that connects the supply line. If the valve turns inside the tank, hold its base with a locking pliers. Tip: Throw a towel on the floor underneath to catch water that will drain from the line. 

8. Remove the locknut that holds the valve to the tank. Push down gently on the valve as you unscrew the nut. Pull out the old valve. 

9. Measure the height of the overflow tube. Measure to the top of the tube, not to any water level label on the tube. 

 10. If the height of your valve is adjustable, set the height before you install the valve. Adjust the height of the new fill valve by holding the base and twisting the top. The height from the base to the CL (critical level) mark should be the height of the overflow tube plus 1 in.

11. Remove the cap, press down to compress the washer and screw on the locknut. Connect the supply line.  Turn the nuts on the supply line finger-tight, then give each another one-half turn with a pliers.  Open the shutoff and flush the valve as shown in Photo 4 above, then reset the cap.  If you see a leak, turn the nut another half-turn.

12. Slip the fill tube onto the fill valve. Clip the angle adapter onto the overflow tube. Then cut the tube to fit and slip it onto the angle adapter.  The fill tube squirts water into the overflow tube to refill the toilet bowl. The water that refills the tank gushes from the bottom of the fill valve.  Finally, turn on the water to fill the tank. Pinch the spring clip and slide the float up or down to set the water level 1 in. below the top of the overflow tube or to the water line marked on the tank (see Photo 2 above).

Solution 2:   Fix the flush valve

When a flush valve causes a toilet to run, a worn flapper is usually the culprit. But not always. First, look at the chain that raises the flapper. If there’s too much slack in the chain, it can tangle up and prevent the flapper from closing firmly.  The chain should have roughly 1/2-in. of slack.

If the chain looks okay, test the flapper as shown in Photo 13. If extra pressure on the flapper doesn’t stop the running noise, water is likely escaping through a cracked or corroded overflow tube. In that case, you have to detach the tank from the bowl and replace the whole flush valve. Since the overflow tube is rarely the cause of a running toilet, we won’t cover that repair here.

13. Push down on the flapper with a yardstick and listen. If the sound of running water stops, the flapper needs replacing. 

If pressing down on the flapper stops the noise, the flapper isn’t sealing under normal pressure. Turn off the water, flush the toilet to empty the tank and then run your finger around the rim of the flush valve seat. If you feel mineral deposits, clean the flush valve seat with an abrasive sponge or ScotchBrite pad. Don’t use anything that might roughen it. If cleaning the flush valve seat doesn’t solve the problem, you need to replace the flapper.

Replacing your flapper may require slightly different steps than we show (Photos 14 and 15).  Your flapper may screw onto a threaded rod or have a ring that slips over the overflow tube. If you have an unusual flush valve, finding a replacement flapper may be the hardest part of the job. To find a suitable replacement, turn off the water to the toilet and take the old one with you to the hardware store. You may not find an identical match, but chances are you’ll locate one of the same shape and diameter. If not, try a plumbing supply store or search online. It helps to know the brand and model of your toilet. The brand name is usually on the bowl behind the seat. In some cases, the model or number will be on the underside of the lid or inside the tank. Matching an unusual flapper can become a trial-and-error process. Even professional plumbers sometimes try two or three flappers before they find one that works well.

14. Remove the old flapper from the ears of the overflow tube and detach the chain from the handle arm.

15. Attach the new flapper to the overflow tube and hook the chain to the handle arm. Leave 1/2 in. of slack in the chain. Turn the water back on and test-flush the toilet.

More information

Fix a double-flushing toilet

Repair a leaking toilet

Toilet seat replacement

Toilet performance and features

New toilet that won't flush well 

Replacing a rotted floor under a toilet 

Signs of poorly vented plumbing waste lines 

Make a small bathroom feel big