central heating overflowing

[pid]

the expansion tank for the central heating system is dripping out of the overflow. the ball cock valve is fully closed and it looks if the water is

coming in to the tank through the open vent ( think its called that). i took the magnet cleaning thing out cleaned that. but don't have a clue about

central heating.

any help
thanks

[Paranoia_uk]

It sounds to me like the CH Pump is located in such a way that you have negative pressure which is sending water up the Vent pipe rather than around the CH circuit. Try turning the pump speed down a notch and see if it makes any difference.

[pid]

thanks mate had BG out yesterday he changed the ball valve and didn't make a difference, then turned the pump down and sorted.
 thanks.