This is a valve located on the water pipe that.
Overflow tank in attic leaking.
Once done refill the tank with cold water.
A leaking overflow on the tank is a common cause of a faulty ball cock which is also known as a float operating valve part 1 or part 2.
Flush the toilet to drain the water.
These type of water leaks are easy to find but also easy to fix if your good at a bit of diy plumbing.
Go into the loft and take the lid off each tank.
A cheaper way to fixing a float operating valve is by replacing the valve but in some cases as experienced the valve is then weaker and no longer under manufactures guarantee.
There are normally two but can be virtually any number depending on the size and type of system you have.
If the leaking overflow pipe is at loft level or protrudes from the eaves of the roof then the source is either the cold water storage cistern or the smaller feed and expansion cistern that supplies the boiler if you have one.
The most common leaks coming through the ceiling from the attic would be the float operating valve followed by a burst pipe due to the cold or a joint on the pipe work that may of been knocked at some point.
To turn the water feed off on a toilet cistern use the isolation valve.
In every attic there should be an isolation valve to the tank so there should be no reason to turn the mains water supply of until the emergency plumber arrives to fix the plumbing.
Use a flat head screwdriver to turn the screw a quarter turn clockwise.
Take the lid off each tank and check how high the water level is in each one.
Water leaks occur through roof failure ice dams and water condensation or frost build up inside an attic.
Your central heating system might also benefit from a powerflush to clear out any sludge debris or rust that s blocking the water from flowing properly.
When removing the sludge try not to disturb the water too much as it could end up making its way down the overflow pipe.
In all cases if you do not know which is the problem cistern then a visual inspection will tell you.
The water level in a tank is too high so it is running out the overflow.
