Dripping overflow not ballcock

[Karen Mc]

Hi hopefully someone can advide me on this matter . I got new complete new bathroom refurbished ths next day overflow outside started dripping. As usual company said not there problem to check ballcock which i have by plumber nothing wrong with this . I am really looking for a different answer on what to do . Thank you

 

[Ben-gee]

What’s the ‘overflow’ from?
Cold water tank, central heating feed & expansion tank, unvented cylinder, water softener, toilet, boiler?