I have always thought that drinking hot water from the tap is not a good idea or putting water from the hot water tap in the kettle for boiling for tea etc.
Is this true and why? what is in the hot water that makes it bad - copper from tank?
Tell me this - why does the 'hot' water need to go into a tank in the attic before it goes into the cylinder for heating? Why cant it go straight from the mains to the cylinder?
The storage tank in the attic is there to ensure that the hot water cylinder doesn't run dry.
If you have a combination boiler, the hot water needs are supplied direct from the mains as is your cold water. There is no hot water cylinder involved in this type of system, so you only heat the water you require.