radiators on ,turn bath on no hot water?

we have a vaillant turbo boiler when we have the heating on and try to run a bath the bath water runs cold,the only way we can fill the bath is if let the water trickle out this takes ages .Is there a solution to the problem cheers.
Alan Fenwick, March 2006


done
that was in 2006 hope you fix it by now power flush heat exchang

ed, January 2014
Diverter Valve

James, March 2006
link Click here to see other fixes for Vaillant.