I recently moved into a house with a gravity fed CH system, the Baxi
back boiler is 4-5 years old but the heating system looks much older,
each rad (except the one in the bathroom) has a thermostatic valve and
there is one room stat in the hall.

As everyone knows, with this type of system it is not possible to run
the heating without the hot water.

My problem is that I have been running the heating on "constant" over
the weekend and as a result the hot water is scalding hot to the point
where steam and water have been jetting into the header tank - my loft
sounds like the local branch of Starbucks and the wooshing and banging
is not only getting on my wick but I'm sure it's not doing the system
any good.

I recently replaced the ballcock on the header tank as this kept
overflowing, it still overflows so I guess it's the hot water cylinder
that's up the chute! and I will have to replace this.

At the same time I am considering modifying the system so that the
heating can be run independant of the hot water and maybe zoning the
upstairs and downstairs.

I would like to ask if anyone has anyone undertaken this (or a
similar)job and if they have any tips/tricks/do's dont's/information
on parts/suppliers etc that may help me decide the best way to do
this.

Thanks in advance,

Kev