Why use a programmable room stat if there is already a 2 channel
programmer, surely a standard wireless stat will suffice.

Several reasons. Basically, the advantages of using a programmable stat over
a separate stat and programmer a

1. Controls are in the living area rather than in a manky undersink cupboard
or inaccessible airing cupboard. This enables manual override and
programming to be easily achieved.

2. Rather than turning off completely, the stat can just turn down the
temperature, to say, 12C, ensuring that the house doesn't get freezing
overnight, or whilst you are out.

3. Complex control laws can be used that can predict the house's response to
heat, enabling temperature overshoot to be controlled and enabling the
device to predict how long before the required start period the heating
needs to be on.

The spur that turns off the heating could quite easily do that. And it
is unlikely anyone will have to traipse round to find the room stat,
surely it would be where you screwed it on the wall?

The spur will also turn off the hot water, which may not be desired. If you
are fiddling around with the system whilst testing, you don't want to have
to frequently disappear down the stairs to turn the thermostat on and off
when the nearby programmer can do the same function for pennies more than a
single channel.

Christian.