Thermostats with OpenTherm control bus

OpenTherm

— control standard used mainly in heating boilers. Noticeably inferior to other options in the sense that only two devices can be present on one bus — a control and a controlled one; for complex systems OpenTherm is not suitable. However, this control bus also has quite practical advantages: it allows you to control the temperature not just by turning the boiler on and off but by smoothly changing the power of the gas burner. It allows you to smooth out temperature fluctuations as much as possible, optimize the operation of the heater and reduce its wear.

Compatibility with OpenTherm can be found in different manufacturers; and some EMS (mainly from Bosch) combine this bus support with EMS support (original, not EMS Plus).