A couple of months ago I received the common call: "MOM... The toilet is running...and it doesn't stop!" After removing the tank lid, I could see the exact cause of the problem:
The float arm was broken.
I tried to fix it by only replacing the float arm (cheap, I know), but it was impossible to get rid of the small rusted pieces where the float arm connects to the ballcock. So, instead of only replacing the float arm I went ahead and replaced the whole ballcock with a fill valve, in the end it's going to save us water and troubles later on.
A month later, the same problem popped in my bathroom, the lift trap kept on getting tangled with the rusted pieces on the float arm, preventing the flush valve to close, another running toilet! Look how bad it was:
Once again, it was time to get a fill valve, I used the Fluidmaster Universal Toilet Fill Valve, no metal components :)
Other materials, tools you'll need:
-Wrench or pliers
-Thread seal tape
First, turn off the water supply and flush the tank.
In order to get an easier work area, the metal flanged tubing was completely disconnected. The lock nut or flapper was then removed using a wrench.
Go ahead and remove the old ballcock and float ball. Keep a bucket underneath if you still have water in the tank.
It's now a good opportunity to clean that tank.
Using a x-acto knife score the cone out of the shank washer. Place the shank washer on threaded shank of the new valve. The flat surface sits against the valve.
Install the new fill valve making sure the critical level mark on the valve is at least 1" above the top of the overflow pipe (it can be adjusted, even though I didn't have to do that).
Position the valve where the fill valve nipple is in direct position to the overflow pipe. Push down on the valve shank...
While hand tightening the lock nut underneath the tank. Do not over-tighten or the tank may crack.
I decided to change the metal flanged tubing for a vinyl/braided connector.
Using the coupling nut, the connector was then installed, using thread seal tape as an extra precaution to prevent leaks.
Finally, the refill tube needs to be inserted down into the overflow pipe, making sure it sits above water level, cut it with the scissors if necessary. The other end is then connected to the fill valve nipple.
You can now turn on the water supply.
Take a big breath without worrying about water running after you flush the toilet.
There are many kinds of toilets, all of them with different mechanisms, the fill valve I used comes with complete instructions for different situations you may encounter, there were some extra parts in the kit I didn't need.
It was an easy and still very economical way (around $15), to extend the life of the toilets.