Adam,
I have a friend who has an impressively automated house and you might 
want to aim at something a bit more sophisticated.
First of all the user interface. He has an old smartphone with a 3d 
printed holder which makes a smart control mounted on the wall. He has a 
nice user interface which his wife his pleased with. He also stores his 
data so he can see how the system is performing.
You might want to control each individual radiator and zone the house 
with an individual temperature sensor and power relay. The bathroom 
would be the obvious room to zone.
I also had this fantasy a few years ago and with the help of a lot of 
research manged to hack a windows programme that could monitor and 
control my Vailliant boiler and wrote a programme for the Raspberry PI.
The idea was to make it smart so that I would record inside and outside 
temperatures and over a period of time learn about the heating 
charactersitics so I could set the time when I wanted the temperature 
and not just switch on the system according to the time. So it would 
calculate the time required based on outside temperatures and switch on 
accordingly. Also if the sun was up and temperature was rising rapidly 
it would switch off prematurely.
Ultimately it would be combined with weather data for maximum efficiency.
The project stalled when I discovered that I and my wife worked at home 
and we have the heating on all the time. Am hoping to get back to 
finishing it soon before climate change renders the project useless.
Overt the years I have installed cat 5 cabling in the house with a view 
to monitoring each room. I have also been collecting the white plastic 
containers that dental floss come in to house the temp sensors for 
several years.
I hope that the move to France is successful and your heating 
requirements are probably reduced.
Best Regards
Roger
On 18/02/2019 10:37, Adam John Trickett via Hampshire wrote:
> Bonjour !
>
> I have finally found a use for a Raspberry Pi...! Since moving to France we
> have ended up with a house with stupid electrically heated oil filled
> radiators. They are not properly controlled and quite inefficient, at best you
> can control them on a thermostat but there is no clock...
>
> It seems obvious that all I need is a thermometer, a mains relay a Raspberry
> Pi and some some software to create a time controlled thermostat that I can SSH
> into...!
>
> So I think I need
> a box
> a AC/DC transformer for the Pi
> a mains relay
> a digital thermometer
> an override switch
> something to mount the relay and transformer on
> WiFi Pi or WiFi module for Pi depending on model
>
> I think this is technically easy to do, but the biggest constraint seems to be
> that the overall box needs to be small and "wife friendly"...
>
-- 
Please post to: Hampshire@???
Web Interface: 
https://mailman.lug.org.uk/mailman/listinfo/hampshire
LUG URL: 
http://www.hantslug.org.uk
--------------------------------------------------------------