Toilet tank that won't stop filling

[lpassler]

I recently moved into an older home. The toilet in the basement has a leak from the tank to the bowl (food colouring test worked immediately). I was attempting to replace the flush valve, thinking that this was the source of the problem. The flapper itself is clear of build up or material that would cause water to leak directly from the flapper.

I ran into the first snag when I wasn't able to turn off the water to the toilet - just will not budge. I decided that, until I get a plumber to change/repair shut-off valve, I would turn off the water main and proceed.

I turned off the water, flushed the toilet, used towels and rags to dry tank. In the time it took me to re-read the installation instructions and take the new part of of its package, I found water in the tank again. Barely a puddle, but water.

I dried the tank again. Waiting 20 minutes. There's water in there again.
I haven't even tried to remove the badly rusted mounting bolts because the tank won't stop filling.

Any suggestions? Where is the water coming from with the house's water turned off? Just residual water in the lines between the main and the toilet?

[HayZee518]

any water ABOVE the basement toilet will flow down by gravity. the ball cock is naturally open because its float has dropped, opening the ballcock's valve. your whole system will need to be drained to replace the straight or angle stop at the basement toilet. if you have a gas hot water tank, turn the main gas control knob to pilot position. if its electric shut off the breaker before you drain the system.

[lpassler]

Thanks for that.
I waited an hour and very little water entered the tank, so I see what you mean. I might tackle this later this afternoon (when it's too hot to work outside... no shortage of projects moving into an older house).

I appreciate your speedy response, by the way!