Secondly, ensure that you have a cylinder thermostat. It sounds like you
have an S plan system. If no cylinder stat is present, you need to insert it
in series between the programmer "HW On" output and the hot water zone valve
motor live (normally brown) wire.

Right. NOw you've lost me. Where can i find out what an 's' plan
system is? Why do i need a cylinder stat if i dont have one at the moment?

By the sounds of it there should be a cylinder stat, if there isn't
one it would be required to modulate the hot water temp. If you don't
have one at the mo you wont really see any benefits by having
efficient heating controls if the rest of the system is innefficient.
If you're thinking of entirely rewiring your heating system I would
have thought you would be able to tell what sytem you have.
If it is an S plan there should be the boiler flow coming into the
airing cupboard, through the pump, then teeing into two valves. The
outlet of the heating valve will go into the heating flow. The outlet
of the water valve will go to the HW tank.


SJW
A.C.S. Ltd.