In need of a good thermostat for my boiler, I investigated about the models and technologies available.

The requirements were :

  • Reliable & Safe (I don't think it's a 230V commutation (more around 24V) but still...)
  • Voltage-free contacts
  • Programmable over 7-day
  • At least 4 settings per day (on/off morning + on/off evening)
  • Programming times with 1/2 hour steps max
  • Wireless if possible
  • Autonomous (no obligation for the Raspberry Pi or any other micirocontroller to be on)
  • Connectable to a home automation system if possible
  • Remotely programmable if possible
  • Remote override of settings if possible

Trouble is, the perfect thermostat doesn't seem to be available in France. During my investigations, I found the following options :

  • Wired option: Cheap but not wireless and not connectable to an external system
  • Proprietary wireless: Usually not connectable either
  • Wifi thermostats - local server: The best (on the paper) seems the one from Heatmiser but they can be quite expensive, need permanent 230V and are wall mounted. Moreover they don't seem to be distributed in France. But the API is documented.
  • Wifi thermostats - cloud: The latest trend: Nest, Tado°, Netatmo, etc... I DON'T want to rely on a internet connexion to command the heating nor I want to upload private data (being in or out) to a private company. Privacy and risk of ending up with a useless piece of hardware if the manufacturer disappears render this solution a no go.
  • Chacon/DI.O/MyFOX: Didn't find anything available
  • EnOcean: Didn't find anything available/suitable
  • Z-Wave: Horstmann/Secure seem to fulfill the requirement

Secure SCS317

Horstmann (the old brand name) seem to appear on all the home automation forum, especially the model HRT4-ZW. Secure (the new name) released recently a model SCS317 (sold as kit paired with the actuator SSR303 under the name SCS318) which is ticking almost all the boxes of my list.


It is a 7 day programmable thermostat with 6 temperatures settings per day, temporary override, holiday mode, TPI (Time Proportional & Integral) and speaks z-Wave.

It also has a ten-minute resolution, so I could programme some heating from 06:40 to 8:20! My old thermostat could only do hours (for example from 07:00 to 8:00).


The main feature is the fact that it is a Z-Wave product so (in theory) compatible with loads of other products and Home Automation boxes. That said, Z-Wave is also very much a proprietary wireless technology (even the access to the API is under NDA!!!!) and seems quite complicated to control from homemade solution. But this will be for next time...