Perhaps your water heater was changed from tank fed to mains fed and the tank removed when the new boiler was installed. The basin probably was on mains all along (safer for drinking) but the bath water from the tank, Also possible:- bath is on cold mains but a control cock below was turned of by someone who meant to deal with the tap dripping but never got round to it, preferring to shower anyway.
Rodge, February 2011
