On Fri, 17 Jun 2011 21:07:28 +0100, Tim Streater wrote:

I assume that these things control the rads directly, i.e. they turn the
TRV on/off as they think the need arises?

Er, no not in the context of this thread so far that is. I think you
can get things that do do what you suggest.

This thread is about a normal programmable thermostat. Generally they
are just a replacement for the traditional bimetal mechanical
thermostat.

What they offer is a temperature profile through the day. For example
at night it will have a set point of say 15C, then in the morning it
could have 19C for a couple of hours then drop back to 15C when
everyone is at work through the day, back up to 18 when the kids come
home and 21C for slobing out infront of the telly after dinner.

They also have a much lower temp range when switching in either
direction (off to on or on to off). Ours keeps the room to the set
point within about 0.5C (1C range), a mechnical stat would be doing
well to keep the room within 2C (4C range) of its set point.

--
Cheers
Dave.