The proposal is for programmable room thermostats and no overall
programmer, just a switch to turn off the entire heating system
(except HWC).

P.S. I don't see the point of not having a programmer instead of a switch.
You probably need one anyway for the hot water side, and a twin channel
isn't much more than a single channel. I suppose some people would find it
simpler to operate a switch, given that the timing function is unlikely to
prove useful.

Christian.