Hi, I'm replacing my existing drafty 30 year old conservatory with
something which might be worth heating. The current central heating
uses a Honeywell CM67 programmable thermostat. I plan to extend this
central heating into the conservatory with a couple of radiators and
put a motorised valve on this new leg of piping, connected to a simple
thermostat (set at comfortable rather than warm) that will shut the
valve when the conservatory is up to temperature (e.g. if it's sunny)
even if the rest of the house is still demanding heat.

I realise that the conservatory might get cold when the rest of the
house is not demanding heat but I can live with that I think, rather
than have a properly zoned system which would require messing with
pipes already laid in concrete floors.

What does anyone think of this plan - will it work?
Any recommendations for the type of valve and stat I'd want on 15mm
piping?

Thanks.