Thanks all for replies.
Mikuwp94 my aim is to control flow of heated water through individual radiators. Certainly stop/start. I would also like the option to slow down flow to enable finer control.
Currently all radiators have manual TRV. I would like to remove the existing heads and replace with electronic TRV’s which are capable of connection to my bespoke system enabling two way communication for control and data collection. Current plan is to have a number of Imps distributed round house to monitor room sensors and control connected devices. A central computer (currently Raspberry Pi) will coordinate, monitor and plan the system.
Hugo’s description of UK central heating system is an accurate description of existing system.
I’ve searched the web and cannot find a TRV with published API, aimed at the hobbyist. This surprises me given the amount of interest there is in home automation. CloudControl, as far as I understand it, http://www.earth.org.uk/open-source-programmable-thermostatic-radiator-valve.html has not yet produced a product, still in the design stages.
Hugo, reverse engineering, if simple, is probably best way forward. I understand I require sniffer software and it captures the conversation. Anyone have experience of this?
Also having a look at the Mac! product hacks Hannez82. Interesting!