British gas installed new combi and removed old backboiler but left the flue?

[flipsnap]

Does anyone know if British Gas should've removed the flu when they removed the old back boiler? Its still there and didn't realise until recently. Could find any specifics in the order, just says remove old boiler.

 

[Last Plumber]

Not necessarily. It would mean removing the liner from above (on the roof) and making the chimney good.
If there is nothing going in there, it won't do any harm to leave it and if there is to be a new fire, then the liner would usually be replaced by the installer.
Just my opinion.