Christian McArdle wrote:

Are there any pitfalls I haven't thought of?
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?