I wish I could find the HN comment by the Honeywell engineer that talks about like 6 different safety features none of the open source DIY thermostats have but I cannot seem to find it anymore. Stuff like

- it needs to lock out instead of continuing to try to start the gas heat so you don't flood the house with gas if the ignition is faulty

- it needs to automatically turn on the heat no matter what if if gets too cold

- it needs a mechanical safety feature to shut itself off if the heat gets stuck on

etc etc

@feld My Netatmo doesn't do all that, and neither do the other thermostats connected to the other boilers I have access to.

Fundamentally, those are things the boiler handles (if it's less than 20 years old), not the thermostat. My boiler, even though it's 10 years old, has all these internal features; it also controls the water temperature, etc.

The thermostat is just for deciding if the house is cold or not - I expect all the other controls to be handled by the burner itself.

In other words, I'm not replacing the internal thermostat (the one that regulates the flow temperature, etc.), just the room thermostat. Besides, my sensor is located very far from the boiler, which is in a separate, ventilated room.

I wonder if this is perhaps a fundamental difference in design between some of the EU and US equipment.

Maybe it's only older equipment in the US that doesn't do this and Honeywell had to build it into the thermostat to cover themselves legally?