"Danny" wrote in message
om...
The
HW tank also has an emersion heater (switched off at present) and a
thermostat located on top - this is set to 60 degrees

This is almost certainly the stat which controls the immersion heater - when
it is switched on - and is thus not doing anything useful at the moment.



What is a zone valve, and what are the controls to make my HW
connections more efficient?


"Zone valve" is a generic term for any automatically operated on/off valve
which controls the flow to different parts - or zones - of the system.

You appear already to have one for the heating circuit - controlled by a
room stat.

You need to add another one into the hot water circuit, and to control it by
a stat strapped to the cylinder. Each of these valves should have a
independent pair of contacts which close when the valve is fully open. These
need to be wired up to control the boiler and pump - so that they only come
on when the demand in either or both circuit is unsatisfied. This saves a
lot of energy otherwise wasted making the hot water unnecessarily hot and
keeping the boiler warm when it's not needed.

You'll see how this all works if you look at the S-Plan details in
http://content.honeywell.com/uk/homes/systems.htm

Roger