That's my approach to heating as well - I'd rather not have Hass directly control the boiler/radiators with relays since in case of failure you could have the s

That's my approach to heating as well - I'd rather not have Hass directly control the boiler/radiators with relays since in case of failure you could have the system either stuck on or off. A network-connected thermostat where Hass merely sends commands to is better since it will still retain some functionality should Hass fail.