Flush the toilet and look for a fill valve leak. Lift up on the float arm when the tank is filling to see if the water stops. Bend or adjust the float arm so the tank stops filling when the water level is 1/2- to 1-in. below the top of the overflow pipe. If the fill valve still leaks, replace it (Photo 3).
Insert the new fill valve into the tank according to the instruction sheet and tighten the locknut a half turn past hand tight. If the fill valve is at its maximum height, but the overflow pipe is still higher than the critical level mark, shorten the overflow pipe with a hacksaw so it's 1 in. lower than the critical level mark on the fill valve.
The mysteries of a running toilet can drive you nuts. Whether you hear water running constantly or cycling on and off, we’ll help you decipher the clues so you can stop most leaks. Hardware stores and home centers carry the parts for almost every repair. One cause of a running toilet is a flapper that doesn't seal. If water from the tank seeps around the flapper and into the bowl, the flapper is probably shot. Test for a leaky flapper as shown in Photo 1.
To replace the flapper, first shut off the water supply valve under the toilet (or the main supply if the valve leaks!). Flush the toilet to drain out most of the water, and unhook the old flapper. Buy a new flapper of the same type and install it according to the instructions on the package. Hook the flapper chain onto the flush lever arm so there’s a little slack when the flapper is closed.
If the flapper doesn’t leak and the water still runs, inspect the fill tube connected to the overflow pipe (Photo 1).The end should be above the water line. If the end is under water, cut it back. Next, inspect the fill valve for visible signs of wear and test the float (Photo 2). If the float is improperly adjusted, the tank water level can rise above the overflow pipe and drain into it. Replace the old fill valve if it doesn’t completely shut off or it hampers the float-arm operation (Photo 3).
Install a new “floatcup”-style fill valve as shown in Photos 4 and 5. Adjust the float according to the package instructions to establish the proper water level. Finish the installation by attaching the flapper chain to the flush lever as described above. Turn on the water and test flush the toilet.