Running Toilet: Find the Cause Before Buying Parts

A running toilet is usually simple, but “replace everything in the tank” is not a diagnosis. Watch what the water is doing and the failed part normally introduces itself.

Take the tank lid off and observe

Do not touch anything at first. Is water flowing over the top of the overflow tube? Is the fill valve repeatedly turning on for a few seconds? Is the flapper fully seated? The pattern matters.

If water is entering the overflow tube

The fill valve is not shutting off at the correct water level or the float is adjusted too high. Many modern valves have an adjustment screw or sliding mechanism. Set the water level to the manufacturer's mark or an appropriate level below the top of the overflow tube.

If the tank slowly loses water

A worn, dirty, warped, or poorly seated flapper can allow water to leak into the bowl. The fill valve then cycles periodically to refill the tank. Check the flapper sealing surface for mineral buildup and confirm the replacement style matches the flush valve.

Check the chain

A chain that is too tight can hold the flapper slightly open. A chain that is too loose can tangle or fail to lift the flapper properly. Leave a small amount of slack when the handle is at rest.

Check the refill tube

The small refill tube should discharge into the overflow tube as designed, but it should not be shoved so far down that it can create siphoning. Use the proper clip and routing recommended for the valve.

When the fill valve itself is worn

If the valve sticks, hisses continuously, will not shut off after adjustment, or has internal seal wear, replacement is often more reliable than repeated adjustment. Shut off the fixture supply, flush the tank, sponge out remaining water, and follow the replacement valve instructions.

After the repair

Cycle the toilet several times, check the tank and supply connections for leaks, verify the refill level, and make sure the toilet stops completely after each flush.