toilet stops running when faucet is turned on

[jaristotle]

The toilet doesn't run very often at all, but if it does, I can stop it from running by turning the sink faucet on. What could this be?

[LazyPup]

When all the faucetts and valves are closed the internal line pressure will be equal with the supply pressure. Whenever a valve or faucett is opened flow begins. The venturi principal states that in a fluid, when the velocity of flow is increased there is a proportional decrease in pressure.

It sounds like the toilet fill valve is in the early stages of failure. When all the water valves are off the line pressure is sufficient to produce a slight blow-by through the valve. When a faucett is turned on, the line pressure drops just below the point of the blow-by. Aside from a very minute amount of water loss there is really nothing to worry about at this time, but in all likelyhood within the next 3 to 6 months you will need to either rebuild or replace the toilet fill valve.

If your toilet has the older ball-cock style valve, which has an arm and a round float ball look on the top of the valve and you will see two screws. You may resolve the problem by tightening the center screw about 1/2 turn.