In an earlier contribution to this discussion,
Grumps wrote:

I assume that with a progammable thermostat (eg.
http://www.screwfix.com/app/sfd/cat/...7585&ts=55860# or
http://www.screwfix.com/app/sfd/cat/...9276&ts=55860# ) it is
possible to leave the central heating timer switched on all the time
and just to control boiler activity using one of these. Horstmann or
Danfoss, any comments as to which is better?

Yes, set CH on the original timer to constant and use the timing function in
the programmable stat to do the actual timing. [The original timer can still
time the hot water, of course]

The Danfoss is a bit more expensive but allows for 6 on-off events per 24
hours - which is useful. I don't know how many the Horstmann does - it
doesn't say.

Both do 5/2 day programmes so that you can do something different at the
weekend. If your life/work pattern is more complicated than that, you may be
better off with a stat which allows a different programme for each day of
the week - such as the Honeywell CM67. The CM67 also has an 'optimum start'
option whereby you tell it the time at which you need the house to be up to
temperature, and it decides when to turn the heating on. More expensive
still, of course, (about 45 quid from RKM Controls) but worth it if you want
the extra features.
http://www.heatingcontrolsonline.co....products_id=67
--
Cheers,
Set Square
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