overflow from eaves?

overflow running can be many reasons depending what tank is overflowing.

check what tank it is.
if it's only doing it sometimes ie when boilers running etc
i would say your problem is more that just the ball valve.
and check when it overflows if the water in the tank is hot or warm.

hi-spec plumbing & heating (essex)
May 2010

the overflow pipe is running cos your header tank is full and the balcock valve is not shutting down the water flow ,take the lid of the tank reduce the water level and repair or replace the ballcock or little washer inside the valve .

joe flowers
May 2010