Overflow from Expansion tank Dripping

[Rudolph_Heller]

I hope someone might explain to me why the overflow from the expansion tank drips in the morning for about an hour after the heating fires up, it then stops and does not drip again during the day.
I have a fully pumped "Y" system as show on the accompanying drawing the dripping occurs on the central heating cycle and when, the hot water circuit is closed.

 

[exedon2]

It's dripping because when boiler on system volume increases due to water expansion .
Level rises in tank overflow drips!
Probably needs new ball valve in tank,
Plus bail some water out of tank to reduce level.

 

[Rudolph_Heller]

It's dripping because when boiler on system volume increases due to water expansion .
Level rises in tank overflow drips!
Probably needs new ball valve in tank,
Plus bail some water out of tank to reduce level.

Thanks for your reply, which make sense to me. Bailing out water alone will not help as ball cock would open and refill tank to previous level, but I will do that and adjust the ball to a lower fill level.
Cheers

 

[ShaunCorbs]

Is there an iso on the ball valve ?

Might be worth turning it off for a day to two see if that solves it then it confirms a new one is required

 

[Rudolph_Heller]

Is there an iso on the ball valve ?

Might be worth turning it off for a day to two see if that solves it then it confirms a new one is required

I can't remember if I fitted one or not, but I can always go back to tying the float up to the roof truss above.