How to fix a perpetually running toilet

When you lift the handle on a toilet you lift the flap inside that lets a
tank-full of water out, but sometimes the toilet doesn’t quit running and
you hear it run and run and run. Luckily there isn’t that much that can go
wrong with toilets and it’s not too expensive to fix them to begin with. Often
the toilet can be fixed my maneuvering an inside part, but first you have
to lift the top off the tank and have a look.

Inside the toilet you’ll see a chain attached to the inside handle which is
fastened to the “flapper” that stops the water. You’ll also see a plastic
float that drops as the water drains. The float is connected to a valve
that lets water into the tank, when the float is down and stops (or should
stop) when the float is up it flows, there’s also an overflow tube in the
middle that drains water out into the bowl if it gets too high. Give it a
couple flushes as you watch the process of what’s happening in the toilet
in order to get to know what’s happening.

If the tank is not filling at all look to make sure the flapper is closing
all the way, or that the chain is not caught either under the flapper or
perhaps has come off and is stopping the flapper from closing in some way. If
you have a ball seal instead of a flapper, is the wire that lifts the ball
straight and does it move freely? If anything seems wrong with the flapper,
just try pushing it back into place to see if that stops it. If the chain
is off or is caught on or under anything, release it so the toilet flows
and then stops at the water line - you’ll know the water line of the toilet
because unless it’s brand new there will inevitably be a water mark where
the water usually rests when full. If the water is not at the water line,
check your water valve to see that it is on all the way. If it is not, turn
it all the way on and your tank should start filling up to the water line
(unless the Refill Valve or Float are not adjusted correctly).

If all is well so far, try adjusting the valve float. Just pull up on the
bulb or floating mechanism with your hand and see if this stops the water
flow, if so then adjust the level of the float so the tank stops filling
when the water is about an inch below the top of the overflow tube. If the
float is around the valve post, pinch the metal clip and slide the float
down on the wire, or if the float is the bulb on an arm, try turning the
screws on top of the valve or bending the arm a little further down to make
it stop. Also, check the small rubber fill tube leading from the valve to
the overflow tube and sometimes the valve itself can act as a siphon. In
that case, adjust the valve height or tube height up, or adjust the water
level down.