Your ballcock is comming on -- replace tank ball or sometimes you have to change out flush valve -- but change tank ball first and see if that will do it You hardly ever have to change flush valve -- Your ballcock is what lets water come into your tank
Turn off the valve & tie up the ballcock...
When you start to unscrew a ballcock, you are essentially loosening the connection between the ballcock and the water supply line. This allows you to either remove the ballcock for maintenance or replacement, or to adjust the float level to control the water level in the tank.
A surge in water pressure can cause this. Also, a defective ballcock would pop off under these conditions. Replace the ballcock and consider installing a pressure reducing valve (PRV) on the incoming water line.
Turn off the water and drain the tank. Sop up excess as needed. Remove old ballcock and install new one. Connect chain and verify slack, but not too much slack, and that the chain will not catch an anything. Turn on water and let tank fill. Flush several times and verify correct operation. Double check chain. Sometimes, the ballcock seat is bad. You can replace it, but that is usually difficult and occasionally gets out of hand. They make a ballcock with seat replacement. The seat sits on top of the old seat using some kind of putty. Ususally, you remove old ballcock, clean and dry seat, apply putty bead to new seat, and press on, following any specific directions in the kit. In all cases, you need to check the minimum drain level. There is a cup on the back of the ballcock that lets you adjust how far down the water goes before the ballcock closes. This can save water. Set it to where the flush is correct for your application.
A ballcock is a ball float on the end of a lever in the water closet of a toilet. As the level of water in the closet rises, so does the floating ballcock. When the water level is high enough, the lever operates a sliding valve and the water coming into the closet is shut off.
Adjust the flow rate to a slower fill through the ballcock in the tank.
That is a fill valve and is part of the ballcock system. When someone pulls the lever, that pulls the chain and lifts the flush valve flapper and empties the tank into the bowl. That causes the float to drop, opening the fill valve and allowing water from the supply to enter and refill the tank.
The water in the lower toilet is probably being siphoned out of the tank by the negative pressure caused by flushing the upper toilet. This CAN happen if the water level in the tank of the lower toilet is over the top of the ballcock. If this is the case, the tank water is being siphoned into your drinking water! Replace the ballcock with a Fluidmaster right away. If you have a small white fill valve that sits in the bottom of the tank, get rid of it. These are illegal and WILL siphon under these conditions. If the lower toilet runs AFTER the fill cycle of the upper toilet, it may be that the ballcock seals at a lower pressure, and the pressure spike when the upper toilet shuts off causes it to run a bit until the added water closes the valve a little tighter.
The water level in the tank is set by the ballcock, the mechanism with the float that is responsible for turning the water on and off when you flush. The water level in the bowl is set by the height of the top of the S-trap that is part of the bowl. Tank water level is adjustable, bowl water level is not.
If you open the lid on your toilet you should see the ballcock. It is normally on the left side and has the float, that looks like a ball, attached to it. It is used to fill the water in the bowl and set the height of the water.
i dont really know sorry